[ruby-core:90135] [Ruby trunk Bug#15357] Unify proc{} and lambda{}.parameters

[ruby-core:90135] [Ruby trunk Bug#15357] Unify proc{} and lambda{}.parameters

[lars]

Issue #15357 has been reported by larskanis (Lars Kanis).

----------------------------------------
Bug #15357: Unify proc{} and lambda{}.parameters
https://bugs.ruby-lang.org/issues/15357

* Author: larskanis (Lars Kanis)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
The current implementation of Proc#parameters [differentiate between lambda? true and false](https://github.com/ruby/ruby/blob/49cd16bfaf4f03885058ce748119bc8ea2de735a/iseq.c#L2800).
This is presumably due to the fact, that [procs use tricks](https://ruby-doc.org/core-2.5.3/Proc.html#method-i-parameters) to apply arguments differently than lambda and methods.

Unfortunately `proc{}.parameters` states all `:req` parameters as `:opt`, so that these both types of parameters are not distinguishable.
This information loss leads to the situation that two different proc signatures return an equal parameters list, but behave differently:

```ruby
pr = proc{|a,b=2| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [:a, 2]  # :a is interpret as the first parameter

pr = proc{|a=1,b| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [1, :a]  # :a is interpret as the second parameter
```

That means that the current return values of `proc{}.parameters` are not suitable to build wrapper or proxy objects for a proc.
In Eventbox I use the workaround to pass the proc to `define_method` and [query the method parameters instead](https://github.com/larskanis/eventbox/blob/3bcbc30096c6003e96d41c6496c781dfc90ac36a/lib/eventbox/argument_wrapper.rb#L10-L17).
That way the list of parameters can be retrieved including `:req` and `:opt` differentiation, so that a wrapper proc can be built.

The application of argument assignment tricks are a property of the Proc object, but not a property of single parameters.
The property of the Proc object is already readable through `Proc#lambda?`, so that there's no need to apply this property to `Proc#parameters` as well.

My proposal is to unify `proc{}.parameters` and `lambda{}.parameters`, so that `proc{}.parameters` returns `:req` arguments as well.




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

[ruby-core:94625] [Ruby master Feature#15357] Proc#parameters returns incomplete type information

[merch-redmine]

Issue #15357 has been updated by jeremyevans0 (Jeremy Evans).

Backport deleted (2.4: UNKNOWN, 2.5: UNKNOWN)
ruby -v deleted (ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux])
Tracker changed from Bug to Feature
File proc-parameters-req-15357.patch added

I don't think the current behavior is a bug, as the parameters for a non-lambda proc are optional.  Also, changing the behavior could be backwards incompatible.

I propose instead a `lambda` keyword to `Proc#parameters`, which would return the parameters as if the proc were a lambda.  Attached is a patch that implements this.

----------------------------------------
Feature #15357: Proc#parameters returns incomplete type information
https://bugs.ruby-lang.org/issues/15357#change-81217

* Author: larskanis (Lars Kanis)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
The current implementation of Proc#parameters [differentiate between lambda? true and false](https://github.com/ruby/ruby/blob/49cd16bfaf4f03885058ce748119bc8ea2de735a/iseq.c#L2800).
This is presumably due to the fact, that [procs use tricks](https://ruby-doc.org/core-2.5.3/Proc.html#method-i-parameters) to apply arguments differently than lambda and methods.

Unfortunately `proc{}.parameters` states all `:req` parameters as `:opt`, so that these both types of parameters are not distinguishable. This information loss leads to the situation that two different proc signatures return an equal parameters list, but behave differently:

```ruby
pr = proc{|a,b=2| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [:a, 2]  # :a is interpret as the first parameter

pr = proc{|a=1,b| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [1, :a]  # :a is interpret as the second parameter
```

That means that the current return values of `proc{}.parameters` are not suitable to build wrapper or proxy objects for a proc. In Eventbox a workaround is used: The proc is passed to `define_method` and the [method parameters are retrieved instead](https://github.com/larskanis/eventbox/blob/3bcbc30096c6003e96d41c6496c781dfc90ac36a/lib/eventbox/argument_wrapper.rb#L10-L17). That way the list of parameters can be retrieved including `:req` and `:opt` differentiation, so that a wrapper proc can be built.

The application of argument assignment tricks is a property of the Proc object - not a property of single parameters. Therefore it shouldn't be applied to `Proc#parameters` in addition - at least not in a way that discards valuable information. The property of the Proc object is already readable through `Proc#lambda?`, so that there's no need to apply this property to `Proc#parameters` as well.

My proposal is to unify `proc{}.parameters` and `lambda{}.parameters`, so that `proc{}.parameters` shows positional arguments without default value as type `:req` as well.


---Files--------------------------------
proc-parameters-req-15357.patch (5.15 KB)


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

[ruby-core:96846] [Ruby master Feature#15357] Proc#parameters returns incomplete type information

[lars]

Issue #15357 has been updated by larskanis (Lars Kanis).


Sorry for my late answer! I didn't get a notification mail.

As noted above: The application of argument assignment tricks is a property of the Proc object - not a property of single parameters. Therefore it shouldn't be applied to `Proc#parameters` in addition to `Proc#lambda?` . I therefore think it's kind of bug.

Nevertheless your patch looks like a good alternative, which keeps backward compatibility and doesn't discard information when called as `proc.parameters(lambda:true)`. Would you still mind to merge it?


----------------------------------------
Feature #15357: Proc#parameters returns incomplete type information
https://bugs.ruby-lang.org/issues/15357#change-83850

* Author: larskanis (Lars Kanis)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
The current implementation of Proc#parameters [differentiate between lambda? true and false](https://github.com/ruby/ruby/blob/49cd16bfaf4f03885058ce748119bc8ea2de735a/iseq.c#L2800).
This is presumably due to the fact, that [procs use tricks](https://ruby-doc.org/core-2.5.3/Proc.html#method-i-parameters) to apply arguments differently than lambda and methods.

Unfortunately `proc{}.parameters` states all `:req` parameters as `:opt`, so that these both types of parameters are not distinguishable. This information loss leads to the situation that two different proc signatures return an equal parameters list, but behave differently:

```ruby
pr = proc{|a,b=2| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [:a, 2]  # :a is interpret as the first parameter

pr = proc{|a=1,b| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [1, :a]  # :a is interpret as the second parameter
```

That means that the current return values of `proc{}.parameters` are not suitable to build wrapper or proxy objects for a proc. In Eventbox a workaround is used: The proc is passed to `define_method` and the [method parameters are retrieved instead](https://github.com/larskanis/eventbox/blob/3bcbc30096c6003e96d41c6496c781dfc90ac36a/lib/eventbox/argument_wrapper.rb#L10-L17). That way the list of parameters can be retrieved including `:req` and `:opt` differentiation, so that a wrapper proc can be built.

The application of argument assignment tricks is a property of the Proc object - not a property of single parameters. Therefore it shouldn't be applied to `Proc#parameters` in addition - at least not in a way that discards valuable information. The property of the Proc object is already readable through `Proc#lambda?`, so that there's no need to apply this property to `Proc#parameters` as well.

My proposal is to unify `proc{}.parameters` and `lambda{}.parameters`, so that `proc{}.parameters` shows positional arguments without default value as type `:req` as well.


---Files--------------------------------
proc-parameters-req-15357.patch (5.15 KB)


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

[ruby-core:96855] [Ruby master Feature#15357] Proc#parameters returns incomplete type information

[eregontp]

Issue #15357 has been updated by Eregon (Benoit Daloze).


I agree, and discussed that a bit in #16499.

I think Proc#parameters should expose source-level information, not interpret it according to Kernel#lambda?.

----------------------------------------
Feature #15357: Proc#parameters returns incomplete type information
https://bugs.ruby-lang.org/issues/15357#change-83865

* Author: larskanis (Lars Kanis)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
The current implementation of Proc#parameters [differentiate between lambda? true and false](https://github.com/ruby/ruby/blob/49cd16bfaf4f03885058ce748119bc8ea2de735a/iseq.c#L2800).
This is presumably due to the fact, that [procs use tricks](https://ruby-doc.org/core-2.5.3/Proc.html#method-i-parameters) to apply arguments differently than lambda and methods.

Unfortunately `proc{}.parameters` states all `:req` parameters as `:opt`, so that these both types of parameters are not distinguishable. This information loss leads to the situation that two different proc signatures return an equal parameters list, but behave differently:

```ruby
pr = proc{|a,b=2| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [:a, 2]  # :a is interpret as the first parameter

pr = proc{|a=1,b| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [1, :a]  # :a is interpret as the second parameter
```

That means that the current return values of `proc{}.parameters` are not suitable to build wrapper or proxy objects for a proc. In Eventbox a workaround is used: The proc is passed to `define_method` and the [method parameters are retrieved instead](https://github.com/larskanis/eventbox/blob/3bcbc30096c6003e96d41c6496c781dfc90ac36a/lib/eventbox/argument_wrapper.rb#L10-L17). That way the list of parameters can be retrieved including `:req` and `:opt` differentiation, so that a wrapper proc can be built.

The application of argument assignment tricks is a property of the Proc object - not a property of single parameters. Therefore it shouldn't be applied to `Proc#parameters` in addition - at least not in a way that discards valuable information. The property of the Proc object is already readable through `Proc#lambda?`, so that there's no need to apply this property to `Proc#parameters` as well.

My proposal is to unify `proc{}.parameters` and `lambda{}.parameters`, so that `proc{}.parameters` shows positional arguments without default value as type `:req` as well.


---Files--------------------------------
proc-parameters-req-15357.patch (5.15 KB)


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