Low-precedence method call syntax for paren-free chaining

[avdi]

Inspired by this discussion, where @jashkenas suggested I file a ticket for it.

Synopsis

Before:

$('some_selector').click (e) -> 
  #... handler code...

After:

$ 'some_selector' .. click (e) -> 
  #... handler code...

Details

Add a new syntax for calling methods with low precedence, suitable for chaining. In the example above I use .., but that's just a suggestion off the top of my head; it could be anything.

Why?

As I'm finally getting a chance to use CoffeeScript for real, I've been immediately struck by two things: the language and conventions strive to avoid extra parenthesis (yay!) but in many common cases that's not completely possible (boo!). As a result, I see a lot of code like the "before" example which mixes paren and paren-free calling. Since I strive for code in which "same things look the same", this was a bit jarring. When I first saw the code above it signaled to me that there was something "special" about the call to jQuery's $() method, since it required parens and the call to .click did not. As it turns out the only thing special about is was that it was not at the end of the line.

The suggested change would enable even more put-the-top-down-and-let-the-breeze-blow-through-your-hair paren-free coding, which I think would be a Good Thing.

[cfcosta]

👍

[elland]

👍

[jonmagic]

👍

[ericallam]

To me, the "before" actually looks a lot better and is more readable. The argument of "making the same things look the same" breaks down because now there are two different syntaxes for calling a function . and .., so this won't actually solve the problem.

[rjungemann]

👍

[showell]

-1

This feature adds complexity to the language, and it's obviously not essential. The ".." syntax feels very cryptic to me, and the only alternative I can think of is, um, parentheses.

[paulmillr]

👎, chainable APIs sucks. https://gist.github.com/1730755

[jashkenas]

Hey folks -- although I've said this before in other tickets ... simply 👍-ing a post doesn't help get features added to CoffeeScript, because the sad reality of Github issues is that they aren't a democracy.

If you think this feature is a good idea, tell us why. If you think it could be improved, tell us how. Or if you think that @avdi's proposal is 100% complete and perfect as it stands, tell us that. ;)

[elland]

good point, @jashkenas. I like the idea of avoiding all parens for methods and I would expect a method chain to be evaluated from left to right just as in Ruby, Obj-C etc., I think the two-dots is a bit cryptic as well, and it looks a bit too much as instance..class_method in Ruby to make me comfortable with it. I think "simple" left-to-right evaluation of a method chain by default could solve the issue.

[yuchi]

I like this proposal a lot more than of the over-engineered proposes of #1495

Correct me if I'm wrong, can this operator can be described as:

.. operator closes every implicit parens opened from the start of the expression.

Cannot wait to be able to do $ '.sel' .. on 'click', '.els', (e) -> false

[elland]

@yuchi it certainly is

[olivierlacan]

The first time I wrote a jQuery selector in CoffeeScript I tried to write:

$ "a:first-child".click (event) ->

While it's hard to tell what @avdi's suggested syntax could cause in the long run, it has one clear disadvantage: not being intuitive at all.

[ericallam]

Won't we still need parenthesis for function calls that don't have arguments? If this proposal wen't through, someone might expect this to work:

$ '#selector' .. hide ..

Turning into this:

$('#selector').hide()

[avdi]

@rubymaverick: that's another very surprising thing about CoffeeScript syntax, and one which I hope will be addressed some day. But that's a discussion for another ticket; and one which I rather imagine you've all talked to death by now :-)

[avdi]

@yuchi: hah, the .. was completely off the top of my head for the sake of an example; funny that someone else used it as well.