[ruby-core:71271] [Ruby trunk - Feature #11537] Introduce "Safe navigation operator"

[alonecomp@gmail.com]

Issue #11537 has been updated by Laurentiu Macovei.


The same discussion happens to be on TypeScript and ES6 worlds.
Using .. instead of ?. or .? because it's way more clear when you are using the ternary ? : operator on the same line.

If it's not a conflict in Ruby syntax perhaps worths looking at 

https://esdiscuss.org/topic/existential-operator-null-propagation-operator#content-65
https://github.com/Microsoft/TypeScript/issues/16#issuecomment-152275052

Posting the markdown info from there: 

This would be amazing operator!! Especially for `ES6`/`ES7`/`TypeScript` - and why not `Ruby` ?

```js
var error = a.b.c.d; //this would fail with error if a, b or c are null or undefined.
var current = a && a.b && a.b.c && a.b.c.d; // the current messy way to handle this
var currentBrackets = a && a['b'] && a['b']['c'] && a['b']['c']['d']; //the current messy way to handle this
var typeScript = a?.b?.c?.d; // The typescript way of handling the above mess with no errors
var typeScriptBrackets = a?['b']?['c']?['d']; //The typescript of handling the above mess with no errors
```
However I propose a more clear one - as not to confuse ? from the a ? b : c statements with a?.b statements:

```js
var doubleDots = a..b..c..d; //this would be ideal to understand that you assume that if any of a, b, c is null or undefined the result will be null or undefined.
var doubleDotsWithBrackets = a..['b']..['c']..['d'];
```

For the bracket notation, I recommend two dots instead of a single one as it's consistent with the others when non brackets are used. Hence only the property name is static or dynamic via brackets.

Two dots, means if its null or undefined stop processing further and assume the result of expression is null or undefined. (as d would be null or undefined).

Two dots make it more clear, more visible and more space-wise so you understand what's going on.

This is not messing with numbers too - as is not the same case e.g.

```js
1..toString(); // works returning '1'
var x = {};
x.1 = {y: 'test' }; //fails currently
x[1] = {y: 'test' }; //works currently 
var current = x[1].y; //works
var missing= x[2].y; //throws exception
var assume= x && x[2] && x[2].y; // works but very messy
```

About numbers two options: Your call which one can be adopted, but I recommend first one for compatibility with existing rules!
1. Should fail as it does now (`x.1.y` == `runtime error`)
```js
var err = x..1..y; // should fail as well, since 1 is not a good property name, nor a number to call a method, since it's after x object.
```
2. Should work since it understands that is not a number calling a property from `Number.prototype`
```js
var err = x..1..y; // should work as well, resulting 'test' in this case
var err = x..2..y; // should work as well, resulting undefined in this case
```


With dynamic names:
```js
var correct1 = x..[1]..y; //would work returning 'test'
var correct2 = x..[2]..y; //would work returning undefined;
```

What do you think folks?

P.S. `foo?.bar` and `foo?['bar']` syntax would work too.

However the using both current `?` `:` operator and `?.` might be very confusing on the same line.

e.g. using `?.` and `?['prop']`
```js
var a = { x: { y: 1 } };
var b = condition ? a?.x.?y : a?.y?.z;
var c = condition ? a?['x']?['y'] : a?['y']?['z'];
```
as opposed to double dots `..` and `..['prop']`
```js
var a = { x: { y: 1 } };
var b = condition ? a..x..y : a..y..z;
var c = condition ? a..['x']..['y'] : a..['y']..['z'];
```

##### Which one does look more clear to you?

----------------------------------------
Feature #11537: Introduce "Safe navigation operator"
https://bugs.ruby-lang.org/issues/11537#change-54644

* Author: Hiroshi SHIBATA
* Status: Closed
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
I sometimes write following code with rails application:

```ruby
u = User.find(id)
if u && u.profile && u.profile.thumbnails && u.profiles.thumbnails.large
  ...
```

or

```ruby
# Use ActiveSupport
if u.try!(:profile).try!(:thumbnails).try!(:large)
 ...
```
I hope to write shortly above code. Groovy has above operator named "Safe navigation operator" with "`?.`" syntax.
Ruby can't use "`?.`" operator.

Can we use "`.?`" syntax. like this:

```ruby
u = User.find(id)
u.?profile.?thumbnails.?large
```

Matz. How do you think about this?




-- 
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