[ruby-core:100635] [Ruby master Feature#17292] Hash Shorthand / Punning

[keystonelemur@gmail.com]

Issue #17292 has been reported by baweaver (Brandon Weaver).

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Feature #17292: Hash Shorthand / Punning
https://bugs.ruby-lang.org/issues/17292

* Author: baweaver (Brandon Weaver)
* Status: Open
* Priority: Normal
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### Set Literal vs Javascript Object Punning

There was a proposal for a Set literal here: https://bugs.ruby-lang.org/issues/16989

```ruby
set = { 1, 2, 3 }
```

...but it was brought up that this is similar to the Javascript Object punning, or Object shorthand syntax:

```js
const a = 1, b = 2, c = 3;

const punnedObject = { a, b, c }
// => { a: 1, b: 2, c: 3 }
```

**Proposition**: I believe we should use brackets (`{}`) for a shorthand Hash syntax similar to Javascript.

### Hash Punning

My first proposal in this feature request is Hash punning, or Hash shorthand:

```ruby
a = 1
b = 2
c = 3

{ a:, b:, c: }
# => { a: 1, b: 2, c: 3 }
```

This syntax avoids the ambiguous syntax of empty block (`{}`) versus empty set (`{}`), and with the presence of Symbols it introduces a distinct syntax that would be easier to parse against.

One potential issue would be mixed syntax:

```ruby
{ a:, b: 2 }
# => { a: 1, b: 2 }
```

### Method Punning

This syntax can also be used for keyword argument and method call punning:

```ruby
def method_name(a:, b:, c:)
  a + b + c
end

a = 1
b = 2
c = 3

method_name(a:, b:, c:)
# => 6
```

I believe this existing syntax for required keywords gives credence to the idea of introducing punning to Ruby, as it's very similar to existing syntax, and therefor feels "Ruby-like".

### Pattern Matching

This syntax is also already present and used in pattern matching, making it already part of the language:

```ruby
case { x: 1, y: 2 }
in { x:, y: }
  { x:, y: y + 1} # new
else
  # ...
end
```

I believe this further justifies the case for punning syntax.



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