Feature #6414: Destructuring Assignment

• Status: Closed
• Assignee: -
• Target version: -

[edtsech (Edward Tsech)]

I mean:

john = {name: "John", last: "Smith"}
{name, last} = john # extract value by key from the hash and set to local variable with same name
name # => "John"
last # -> "Smith"

Useful for ex. for "options" hashes:
def select(options={})
{only, except} = options
...
end

As extra part of this feature can be hash constructing in this way:

name = "John"
last = "Smith"
find({name, last}) # equals to => find({name: "John", last: "Smith"})

I think both really nice to have in Ruby.
Thanks.

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to matz (Yukihiro Matsumoto)

FYI: There is similar (but not same) proposal: [ruby-core:41772]

--
Yusuke Endoh [e-mail]

[marcandre (Marc-Andre Lafortune)]

• File destructuring.pdf destructuring.pdf added
• Category set to core
• Target version set to 2.0.0

Attaching a one-minute slide. It doesn't cover the "construction" part of this request though.

[rosenfeld (Rodrigo Rosenfeld Rosas)]

-1. I'd still like to see Ruby supporting CoffeeScript hash style for this common pattern:

Instead of
a = 1; b = 2; c = {a: a, b: b}

I'd prefer to write just c = {a, b}. The current proposed syntax wouldn't allow such a feature in the future.... :(

By the way, I can't remember what is the current situation of an old proposition to allow things like {"#{interpolation}": value} as well as {'some string': value}.

Was it already accepted? Is there already a slide for it?

[mame (Yusuke Endoh)]

Marc-Andre, your slide is received. Thank you!

Rodrigo, I don't know CoffeeScript, but what is the difference between OP's (second) proposal and yours?

name = "John"
last = "Smith"
find({name, last}) # equals to => find({name: "John", last: "Smith"})

Instead of
a = 1; b = 2; c = {a: a, b: b}
I'd prefer to write just c = {a, b}.

--
Yusuke Endoh [e-mail]

[rosenfeld (Rodrigo Rosenfeld Rosas)]

sorry but I couldn't find the proposal you're talking about, but looking at the examples it seems there is no difference.

But one thing that is supported in CoffeeScript and is not in the examples is to mix both forms. For example, in Ruby, that would mean:

b = 2; d = 4
{a: 1, b, 'c' => 3, d } == { :a => 1, :b => b, 'c' => 3, :d => d }

[mame (Yusuke Endoh)]

Edward Tsech and Marc-Andre Lafortune,

We discussed your slide at the developer meeting (7/21).

We were not sure if we can actually implement this feature in terms
of yacc. Could you create an experimental patch?

Matz was basically positive to the feature itself, but wanted to
focus on surely implementable syntax (with no parser conflict and
with reasonable code).

--
Yusuke Endoh [e-mail]

[trans (Thomas Sawyer)]

So this is a shortcut for?

name, last = john.values_at(:name, :last)

If so, long ago it was suggested Hash#[] support multiple keys:

name, last = john[[:name, :last]]

Not as short as {name, last} = john, but not quite as esoteric either.

If assigning from an array can work, eg.

john = ['John', 'Smith']
name, last = john

Why not hash? So, just

john = {:name=>'John', :last=>'Smith'}
name, last = john

[cjheath (Clifford Heath)]

On 24/07/2012, at 2:20 AM, trans (Thomas Sawyer) wrote:

If so, long ago it was suggested Hash#[] support multiple keys:

name, last = john[[:name, :last]]

I'm very glad this didn't happen. I often have reason to use arrays as hash keys,
and this would make that impossible.

Clifford Heath.

[trans (Thomas Sawyer)]

I made a mistake with that example.

name, last = john[:name, :last]

[rosenfeld (Rodrigo Rosenfeld Rosas)]

I'd much prefer something like this and reserve the {a, b} syntax to be used as a shortcut for {a: a, b: b} like in CoffeeScript in the future...

Also, I find it clearer to read as well

[shyouhei (Shyouhei Urabe)]

• Status changed from Assigned to Feedback
• Assignee deleted (matz (Yukihiro Matsumoto))

This request won't progress without a working proof-of-concept. Feel free to send us your pull request. https://github.com/ruby/ruby

[yhara (Yutaka HARA)]

• Target version changed from 2.0.0 to 3.0

[yhara (Yutaka HARA)]

• Target version changed from 3.0 to 2.6

[naruse (Yui NARUSE)]

• Target version deleted (2.6)

[jeremyevans0 (Jeremy Evans)]

• Status changed from Feedback to Closed

This proposal has basically been implemented, with single-line pattern matching and valueless hash creation syntax:

john = {name: "John", last: "Smith"}
john => {name:, last:}
name # => "John"
last # => "Smith"
p({name:, last:})

[jeremyevans0 (Jeremy Evans)]

• Has duplicate Feature #8895: Destructuring Assignment for Hash added