[ruby-core:61225] [ruby-trunk - Feature #9076] New one-argument block syntax: &.

Issue #9076 has been updated by So Wieso.


I think this would be a really great idea.
Symbol#to_proc is technically a nice solution, but not nice from the esthetically viewpoint. Just have a look how many people are confused by this.
&.a_method makes immediately clear that here a method call is happening. So & must be a (special) object. Context makes pretty clear which object that is, even if you do not know this syntax rule.
I agree that having two solutions is not nice, but only because we implemented a weak solution we should not restrict ourselves to it as there are mightier and more readable ones.

I'd like to remark, that getting a solution that solves this issue once and for all in official ruby would be much nicer than the current half-hearted .to_proc hack. There are many projects in the Internet that tried to solve this, thus demand is given. Let's unify them!
https://github.com/rapportive-oss/ampex
https://github.com/danielribeiro/RubyUnderscore
https://github.com/raganwald/homoiconic/blob/master/2012/05/anaphora.md
https://bugs.ruby-lang.org/issues/8987 (my request)

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Feature #9076: New one-argument block syntax: &.
https://bugs.ruby-lang.org/issues/9076#change-45573

* Author: Ary Borenszweig
* Status: Feedback
* Priority: Low
* Assignee: 
* Category: core
* Target version: Next Major
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Hello,

I'd like to introduce a new syntax for blocks that have one argument.

Currently you can do this:

[1, 2, 3].map &:to_s

With the proposed syntax this will be written as:

[1, 2, 3].map &.to_s

Instead of ":" we use a ".".

The idea is that this new syntax is just syntax sugar that is expanded by the parser to this:

[1, 2, 3].map { |arg| arg.to_s }

This new syntax allows passing arguments:

[1, 2, 3, 4].map &.to_s(2) #=> ["1", "10", "11", "100"]

It also allows chaining calls:

[1, 10, 100].map &.to_s.length #=> [1, 2, 3]

You can also use another block:

[[1, -2], [-3, -4]].map &.map &.abs #=> [[1, 2], [3, 4]]

Pros:
- Doesn't conflict with any existing syntax, because that now gives a syntax error, so it is available.
- Allows passing arguments and chaining calls
- It's *fast*: it's just syntax sugar. The "&:to_s" is slower because the to_proc method is invoked, you have a cache of procs, etc.
- It looks ok (in my opinion) and allows very nice functional code (like the last example).

Cons:
- Only supports one (implicit) argument. But this is the same limitation of "&:to_s". If you want more than one argument, use the traditional block syntax.
- It's a new syntax, so users need to learn it. But to defend this point, users right now need to understand the &:to_s syntax, which is hard to explain (this calls the "to_proc" method of Symbol, which creates a block... vs. "it's just syntax sugar for")

What do you think?

We are using this syntax in a new language we are doing, Crystal, which has a syntax very similar to Ruby, and so far we think it's nice, simple and powerful. You can read more about it here: http://crystal-lang.org/2013/09/15/to-proc.html



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