[ruby-core:39539] [Ruby 1.9 - Feature #5321][Open] Introducing Numeric#exact? and Numeric#inexact?

[ruby-core:39539] [Ruby 1.9 - Feature #5321][Open] Introducing Numeric#exact? and Numeric#inexact?

[Kenta Murata]

Issue #5321 has been reported by Kenta Murata.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Open
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: core
Target version: 2.0


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40514] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alexey Muranov]

Issue #5321 has been updated by Alexey Muranov.


I like this proposal. -Alexey.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Open
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40519] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Charles Nutter]

Issue #5321 has been updated by Charles Nutter.


Why is BigDecimal considered inexact? Unlike a float, a value in a BigDrcimal is always represented exactly. The value itself may be and estimate for various reasons (irrational, repeating, ...), but that is a property of the value, not a property of BigDecimal. Or put another way, BigDecimal is not inexact since if it is possible to exactly represent the number in base 10, BigDecimal can represent it exactly.

Perhaps the idea of inexact is too fuzzy here...even Float can be exact if the value can be exactly represented in base 2 decimal form with Float's precision.

It seems to me that the interesting characteristic of these classes is not whether the value they represent is exact, but whether arithmetic operations using them can be done exactly. By that definition, only Float is clearly inexact; even if the two operands of a floating-point arithmetic operation are exact, the result may not be. The other types do not have this property.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Open
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40524] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alexey Muranov]

Issue #5321 has been updated by Alexey Muranov.


Charles, this is from the documentation of BigDecimal: "If a computation results in a value which is too small to be represented as a BigDecimal within the currently specified limits of precision, zero must be returned.".
Thus the operations on BigDecimal are not exact. (See also BigDecimal::ROUND_MODE.)

For me it is easier to think simply whether a class is *intended* to represent numbers exactly. The formal definition of exactness probably is the following: "Each operation must be carried out exactly or return NaN or nil, or return some other *exceptional* value."

-Alexey.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Open
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40553] Re: [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alex Young]

On 30/10/11 12:29, Alexey Muranov wrote:
> 
> Issue #5321 has been updated by Alexey Muranov.
> 
> 
> Charles, this is from the documentation of BigDecimal: "If a computation results in a value which is too small to be represented as a BigDecimal within the currently specified limits of precision, zero must be returned.".
> Thus the operations on BigDecimal are not exact. (See also BigDecimal::ROUND_MODE.)
> 
> For me it is easier to think simply whether a class is *intended* to represent numbers exactly. The formal definition of exactness probably is the following: "Each operation must be carried out exactly or return NaN or nil, or return some other *exceptional* value."

The problem with this is that the values *are* exact, and *some* of the
operations are inexact.  Some of the operations are *sometimes* inexact.
 Flagging a class at a time as exact or inexact just sounds wrong to me.
 Better would be flagging values that have had inexact operations
performed on them (or exact operations with an inexact operand) at any
time in their history, but I've no idea how you'd do that while keeping
any sort of respectable performance.

-- 
Alex

> 
> -Alexey.
> ----------------------------------------
> Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
> http://redmine.ruby-lang.org/issues/5321
> 
> Author: Kenta Murata
> Status: Open
> Priority: Normal
> Assignee: Yukihiro Matsumoto
> Category: 
> Target version: 
> 
> 
> Ruby has several numeric classes such as Integer.
> These classes are classified whether their instances represent numbers exactly.
> According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
> The exactness of a Complex depends on its real and imaginary parts.
> 
> Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
> So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
> I want simple way to examine the number exactness.
> 
> I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.
> 
> 
> 

[ruby-core:40555] [ruby-trunk - Feature #5321][Assigned] Introducing Numeric#exact? and Numeric#inexact?

[Yusuke Endoh]

Issue #5321 has been updated by Yusuke Endoh.

Status changed from Rejected to Assigned

Oops, sorry, I've closed this ticket by error.  Reopen.

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40556] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Yusuke Endoh]

Issue #5321 has been updated by Yusuke Endoh.


Hello,

2011/9/14 Kenta Murata <muraken@gmail.com>:
> Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
> So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
> I want simple way to examine the number exactness.

Can you show any actual use case?

-- 
Yusuke Endoh <mame@tsg.ne.jp>
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40557] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alexey Muranov]

Issue #5321 has been updated by Alexey Muranov.


I misread the proposal, it was actually about adding instance Numeric#exact method, and not class Numeric.exact method.

For me, adding class method Numeric.exact? would be good enough.
To examine the exactness of a value, it would be enough to call `val.class.exact?`.
As Alex pointed out, this is better for performance, and it seems easier to assume that Float is always inexact than to inspect its instances.

I think it helps distinguishing classes that are *intended* to represent numbers exactly from those that are not.  Those that are intended for this, should carry out standard arithmetic exactly, or return an exceptional value.

Sorry, i change my mind, i am more in favor of `Numeric.exact?`.  A new subclass of Numeric can implement `Numeric#exact?`, or maybe interval arithmetic would even be better (http://en.wikipedia.org/wiki/Interval_arithmetic).

-Alexey.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40558] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Kenta Murata]

Issue #5321 has been updated by Kenta Murata.


Charles Nutter wrote:
> Why is BigDecimal considered inexact?

As Alexey pointed out, the reason is from BigDecimal's definition.
A BigDecimal represents an *approximation* of a real number, not a rational number.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40559] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[tadayoshi funaba]

Issue #5321 has been updated by tadayoshi funaba.


i've proposed this before 1.9.
and i've virtually used those predicates in Complex/Rational internally.

i've taken those from scheme.
scheme's one accept also complex number.
i think those should be instance methods.

> (exact? 1+0i)
#t
> (exact? 1+0.0i)
#f

bye

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40565] Re: [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Yusuke Endoh]

Hello,

2011/10/31 tadayoshi funaba <redmine@ruby-lang.org>:
> i've taken those from scheme.
> scheme's one accept also complex number.
> i think those should be instance methods.

I guess Scheme's exactness differs from this proposal.
Scheme's exactness is orthogonal to the type.  Actually, the spec of
Scheme allows an "inexact integer" and "exact real."
So it makes no sense to quote Scheme.

But I don't mean that I'm against the proposal.  I think the proposal
is fine even if it is different from Scheme's.

-- 
Yusuke Endoh <mame@tsg.ne.jp>

[ruby-core:40560] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Kenta Murata]

Issue #5321 has been updated by Kenta Murata.


Yusuke Endoh wrote:
> Can you show any actual use case?

I want to create a mathematical function which behaves like 1/x.
This function is defined over real numbers except for zero,
because lim_{x -> +0} 1/x = +inf while lim_{x -> -0} 1/x = -inf.
So I want to raise Math::DomainError for the function with exact zero.
But I don't want to raise the error for inexact zeros, such as 0.0, -0.0,
BigDecimal("0"), and others which are instances of classes I don't know.

If Numeric#inexact? and Numeric#exact? are given,
I can realize the function more easily.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40563] Re: [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Yusuke Endoh]

Hello,

2011/10/31 Kenta Murata <muraken@gmail.com>:
> I want to create a mathematical function which behaves like 1/x.
> This function is defined over real numbers except for zero,
> because lim_{x -> +0} 1/x = +inf while lim_{x -> -0} 1/x = -inf.
> So I want to raise Math::DomainError for the function with exact zero.
> But I don't want to raise the error for inexact zeros, such as 0.0, -0.0,
> BigDecimal("0"), and others which are instances of classes I don't know.
>
> If Numeric#inexact? and Numeric#exact? are given,
> I can realize the function more easily.


Thank you for the explanation.

You expect that 1/x does never raise any exception if x is an
inexact number, right?  I wonder if the expectation is valid.

But anyway, your use case is certainly convincing for me.
Thank you.

-- 
Yusuke Endoh <mame@tsg.ne.jp>

[ruby-core:40561] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alexey Muranov]

Issue #5321 has been updated by Alexey Muranov.


Kenta Murata wrote:

> So I want to raise Math::DomainError for the function with exact zero.
> But I don't want to raise the error for inexact zeros, such as 0.0, -0.0,
> BigDecimal("0"), and others which are instances of classes I don't know.

In my opinion, checking `x.class.exact?` would be good enough.  If you will be checking the instance property #exact? for inputs, you are likely to find most input floats inexact, if they were produced as output of other operations, as operations on floats are not *intended* to be exact.  I think that all exact values should be grouped in separate classes, like Rational, distinguished by their *intended* use.  (Isn't the different intended uses the reason to have more than one class?)  It may make sense to me to create a subclass of Numeric where each value is exact or inexact.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40566] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Kenta Murata]

Issue #5321 has been updated by Kenta Murata.


Alexey Muranov wrote:
> In my opinion, checking `x.class.exact?` would be good enough.

I don't think so for two reason.
First, I think the form of "x.class.exact?' isn't ruby way, and too long than "x.exact?".
Second, it limits the exactness property for class.

Numeric classes including both exact and inexact instances should be allowed, I think.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40567] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[tadayoshi funaba]

Issue #5321 has been updated by tadayoshi funaba.


>But I don't mean that I'm against the proposal. I think the proposal is fine even if it is different from Scheme's. 

i'm ok too, even if you don't understand at all what i mean.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40570] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[Alexey Muranov]

Issue #5321 has been updated by Alexey Muranov.


Kenta Murata wrote:
> Alexey Muranov wrote:
> > In my opinion, checking `x.class.exact?` would be good enough.
> 
> I don't think so for two reason.
> First, I think the form of "x.class.exact?' isn't ruby way, and too long than "x.exact?".
> Second, it limits the exactness property for class.
> 
> Numeric classes including both exact and inexact instances should be allowed, I think.

I am not against Numeric classes including both exact and inexact instances :).  I just doubt it is a good idea to define this in the Numeric class itself, it would looks too heavy for me. (Being able to check whether a given integer is exact? does not look valuable to me.)  It sounds like what  Yusuke Endoh  said about exactness in Scheme (which i do not know).  This would probably mean that you need to set the exactness flag for the first time when you read a value from the input, or it should be set to inexact by default (or, even worse, to exact or inexact depending on the default for the class), which will make you think if your output is inexact because an inexact operation was carried out, or because the exact flag was not set correctly on the first input.  I see benefit in being able to mix exact and inexact values, but it can be done even if exactness is defined on the (sub)class level.  Keeping track of what influences exactness of your value seems easier if you kno
 w that it is a class property.  I think this is all i had in mind.
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:40622] [ruby-trunk - Feature #5321][Assigned] Introducing Numeric#exact? and Numeric#inexact?

[Masaya Tarui]

Issue #5321 has been updated by Masaya Tarui.

Status changed from Rejected to Assigned

maybe miss operation
----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
http://redmine.ruby-lang.org/issues/5321

Author: Kenta Murata
Status: Assigned
Priority: Normal
Assignee: Yukihiro Matsumoto
Category: 
Target version: 


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://redmine.ruby-lang.org

[ruby-core:49681] [ruby-trunk - Feature #5321] Introducing Numeric#exact? and Numeric#inexact?

[mame (Yusuke Endoh)]

Issue #5321 has been updated by mame (Yusuke Endoh).

Target version set to next minor


----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-33199

Author: mrkn (Kenta Murata)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: next minor


Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.



-- 
http://bugs.ruby-lang.org/

[ruby-core:94087] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[merch-redmine]

Issue #5321 has been updated by jeremyevans0 (Jeremy Evans).

File numeric-exact-5321.patch added

Attached is a patch to implement `Numeric#exact?`.  This returns true for Integer and Rational, and false for Float and BigDecimal.  For Complex, it returns true if the real and imaginary parts are both true, and false otherwise (one reason `exact?` needs to be an instance method and not a class method).

This feature is necessary to fix #5179, as BigDecimal is not a core class and Complex cannot know whether or not it is exact.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-80318

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96652] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[wishdev]

Issue #5321 has been updated by wishdev (John Higgins).


I really think this is a very overblown issue that is being handled incorrectly.

First, we have what appears to be a singular issue on our hands

Complex(1, BigDecimal("0.0")).to_r

Whether or not that qualifies as a valid operation. BigDecimal('0.0') is ABSOLUTELY without any question at all an exact number and therefore valid in the original operation.

BigDecimal('0.0') is and ALWAYS is an exact number

An example with a slightly different number (0 does not allow for many calculation examples).

# Request arbitrary precision for future CALCULATIONS
BigDecimal.limit(3)
# => 0
# Store a number
a = BigDecimal('0.00000001')
=> 0.1e-7
# Calculate
a + 0.1
# => 0.1e0 # Note the precision dropped

# Remove the limit
BigDecimal.limit(0)
=> 3
# Recalculate
a + 0.1
# Precision held
=> 0.10000001e0

The number is 100% accurate - the precision only affects calculation results and they are only affected at my request.

(BigDecimal('6e-1092837') + BigDecimal('1')).to_s.length
# 1092842

That is an accurate calculation to whatever required precision exists. You can lock your system up if you increase the length of the number - it will work to accomplish what you ask of it.

One cannot throw out valid concepts because someone offers up convenience methods to developers to limit precision if desired. But the choice is that of the developer and not an issue with the class. The class is fully compliant with exactness and should be afforded that.

Floating point does not offer up a choice - it has intrinsic limits - BigDecimal offers no such limitations.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83622

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96861] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[akr]

Issue #5321 has been updated by akr (Akira Tanaka).


I think associating class with exactness is wrong idea.

Please define the exactness of numeric classes, at first.

I think exactness and inexactness is a property of a method, not class.

For example, Integer#+ is exact because it implements mathematical addition exactly (except memory limitation).
Rational#+ is also exact.
As far as I know, BigDecimal#+ also implements mathematical addition exactly.
But Float#+ is inexact because it implements just approximation of mathematical addition.
(So, mathematically invalid result, such as 1.0 + 1e-20 == 1.0, is possible.)

Subtraction and multiplication is same as addition.
(Integer, Rational and BigDecimal are exact but Float is inexact.)

Division is interesting.
Integer#/ is exact as integer division. (But inexact as normal division.)
http://mathworld.wolfram.com/IntegerDivision.html
Rational#/ is exact as normal division.
But Float#/ and BigDecimal#/ is inexact.

I doubt the concept of "exactness of numeric classes".
So, I against this proposal until someone provide a good definition of
exactness of numeric classes.




----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83874

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96863] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[sawadatsuyoshi]

Issue #5321 has been updated by sawa (Tsuyoshi Sawada).


akr (Akira Tanaka) wrote:
> I think associating class with exactness is wrong idea.
> ...
> I think exactness and inexactness is a property of a method, not class.

But notice that these operations are binary operations, not unary. You cannot talk about just `Integer#+` or `Float#+`, etc. You have to think about integer + integer, float + integer, float + integer, float + float, etc. And float + integer and float + integer are the same as float + float with respect to exactness. The reason should be attributed to some kind of hierarchy between the class; float is less exact than integer, and the exactness of + would be the minimum exactness of the operands.

Hence, at least, the classes should also need to carry some kind of notion of exactness.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83876

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96864] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[akr]

Issue #5321 has been updated by akr (Akira Tanaka).


sawa (Tsuyoshi Sawada) wrote:
> akr (Akira Tanaka) wrote:
> > I think associating class with exactness is wrong idea.
> > ...
> > I think exactness and inexactness is a property of a method, not class.
> 
> But notice that these operations are binary operations, not unary. You cannot talk about just `Integer#+` or `Float#+`, etc. You have to think about integer + integer, float + integer, integer + float, float + float, etc. And float + integer and integer + float are the same as float + float with respect to exactness. The reason should be attributed to some notion of hierarchy of exactness between the classes; float is less exact than integer, and the exactness of + would be the minimum exactness of the operands on both sides.

I see.
I wrongly assumed integer + integer for Integer#+.

> Hence, at least, the classes should also need to carry some kind of notion of exactness.

Do you have good definition of exactness of numeric classes?


----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83877

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96868] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[sawadatsuyoshi]

Issue #5321 has been updated by sawa (Tsuyoshi Sawada).


akr (Akira Tanaka) wrote:
> Do you have good definition of exactness of numeric classes?

Like  alexeymuranov, I misread the proposal. I took it for `Integer.exact?`, etc. instead of `Numeric#exact?`, etc.

As for the notion of **instance method** `exact?` (on numeric instances), I don't think it would be practical. For float, the same number may be exact or inexact depending on its history. The history may include mathematical operations by which it was created, as well as simply as literal interpretation. For example, `2.5` achieved by the following literal may be naturally considered exact:

```ruby
2.5 # => 2.5
```

but the same `2.5` achieved in the following way is inexact:

```ruby
2.5000000000000001 # => 2.5
```

So we may expect it to be possible to have "multiple instances" of 2.5, with different exactness, but that is impossible given Ruby's object system.

As for the notion of **class method** `exact?` (on numeric classes), I think we can define that based on whether the literal interpretation is "transparent". `Float` is not exact because different literals are interpreted as the same instance, as with `2.5` above. I am being careful to use the word "transparent" above, which can be paraphrased as "one-to-one in some relevant sense". `Rational` should be considered exact even though `1/2r` and `2/4r` represent the same instance. `Integer` is exact.

However, the use case that mrkn provided (https://bugs.ruby-lang.org/issues/5321#note-13) requires the instance method `exact?`. I became not so confident with my argument.

----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83881

* Author: mrkn (Kenta Murata)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/

[ruby-core:96899] [Ruby master Feature#5321] Introducing Numeric#exact? and Numeric#inexact?

[matz]

Issue #5321 has been updated by matz (Yukihiro Matsumoto).

Status changed from Assigned to Rejected

Rejected.

Matz.


----------------------------------------
Feature #5321: Introducing Numeric#exact? and Numeric#inexact?
https://bugs.ruby-lang.org/issues/5321#change-83916

* Author: mrkn (Kenta Murata)
* Status: Rejected
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
Ruby has several numeric classes such as Integer.
These classes are classified whether their instances represent numbers exactly.
According to this, Integer and Rational are exact, and Float and BigDecimal are inexact because they're always including error.
The exactness of a Complex depends on its real and imaginary parts.

Now, Ruby's numeric classes doesn't provide predicators to investigate the exactness of their instances.
So, if we want to examine whether a number is exactly zero, we must investigate the class of the number.
I want simple way to examine the number exactness.

I propose to introduce Numeric#exact? and/or Numeric#inexact? for resolving this inconvenience.


---Files--------------------------------
numeric-exact-5321.patch (7.33 KB)


-- 
https://bugs.ruby-lang.org/