Arrow functions and return values
It's a bit unclear to me how arrow functions react to semicolons, for
example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
To me, it seems like this should return undefined. After all, the last
statement in the function is empty. To actually return b * c, you should
drop the semicolon:
var a = (c) = {
var b = 2;
b * c
}
a(4);
This would be consistent with, for example, Rust and would help avoid
annoying accidental returns (see [1] for discussion about this wrt
CoffeeScript).
Cheers,
Jussi
[1] https://github.com/jashkenas/coffee-script/issues/2477
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Re: Arrow functions and return values
Le 29/11/2012 09:41, Jussi Kalliokoski a écrit :
It's a bit unclear to me how arrow functions react to semicolons, for
example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
To me, it seems like this should return undefined. After all, the last
statement in the function is empty. To actually return b * c, you
should drop the semicolon:
var a = (c) = {
var b = 2;
b * c
}
a(4);
I initially only read the 2 snippets and saw no difference. I realized
the dropped semicolon only after reading the text in the middle.
Making a semantic difference out of a present or missing semicolon seems
it would cause a lot of wasted time debugging a program. Especially in
JavaScript where semicolons are optional. JS devs have their eyes
trained to not worry about semicolons (which is probably why I didn't
see a difference at first).
I would expect 8 to be returned in both cases, semicolon or not.
This would be consistent with, for example, Rust and would help avoid
annoying accidental returns (see [1] for discussion about this wrt
CoffeeScript).
I wish JavaScript kept being consistent with JavaScript.
David
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Re: Arrow functions and return values
Jussi Kalliokoski wrote:
It's a bit unclear to me how arrow functions react to semicolons, for
example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
To me, it seems like this should return undefined. After all, the last
statement in the function is empty.
Not by the grammar.
You would need a second ; after b * c; to spell the empty statement.
To actually return b * c, you should drop the semicolon:
var a = (c) = {
var b = 2;
b * c
}
a(4);
This would be consistent with, for example, Rust and would help avoid
annoying accidental returns (see [1] for discussion about this wrt
CoffeeScript).
That's a fine thing in languages like Rust without ASI, which also have
type-checking needs not in JS. JS has ASI and no type-checking, so no-go.
Cheers,
Jussi
[1] https://github.com/jashkenas/coffee-script/issues/2477
CoffeeScript has no way to avoid implicit return, but JS has 'function'
and always will.
/be
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Re: Arrow functions and return values
On Thu, Nov 29, 2012 at 10:32 AM, Brendan Eich bren...@mozilla.com wrote: You would need a second ; after b * c; to spell the empty statement. Interesting fact actually, it would mean the empty statement is no longer a NOOP. It can actually alter a program. I can't think of a situation where this is the case in es5, not counting preventing syntactical errors. But with implicit return values, the empty statement could make the difference. Not sure if this is a problem, just noting that it seems to be a change, one that'll be hard to debug for once implicit returns are heavily used. OTOH people might be tempted to optimize functions by adding an empty statement at the end. Or something. - peter ___ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
Re: Arrow functions and return values
It's a bit unclear to me how arrow functions react to semicolons, for
example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
Hmmm... I was under the impression that arrow functions with normal
function bodies do *not* implicitly return anything. Maybe I need to
adjust my spec goggles, but I don't see that in the latest draft.
Kevin
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Re: Arrow functions and return values
Kevin Smith wrote:
It's a bit unclear to me how arrow functions react to semicolons,
for example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
Hmmm... I was under the impression that arrow functions with normal
function bodies do *not* implicitly return anything. Maybe I need to
adjust my spec goggles, but I don't see that in the latest draft.
Oh (and d'oh!) you are quite right. There's no implicit return or other
TCP aspect save lexical-|this|, at all.
/be
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Re: Arrow functions and return values
On Thu, Nov 29, 2012 at 8:49 AM, Kevin Smith khs4...@gmail.com wrote:
It's a bit unclear to me how arrow functions react to semicolons, for
example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
Hmmm... I was under the impression that arrow functions with normal
function bodies do *not* implicitly return anything. Maybe I need to
adjust my spec goggles, but I don't see that in the latest draft.
This is correct.
var a = (c) = {
var b = 2;
b * c;
}
a(4); // undefined
Rick
Kevin
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Re: Arrow functions and return values
On Thu, Nov 29, 2012 at 9:41 AM, Brendan Eich bren...@mozilla.org wrote:
Kevin Smith wrote:
It's a bit unclear to me how arrow functions react to semicolons,
for example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
Hmmm... I was under the impression that arrow functions with normal
function bodies do *not* implicitly return anything. Maybe I need to
adjust my spec goggles, but I don't see that in the latest draft.
Oh (and d'oh!) you are quite right. There's no implicit return or other
TCP aspect save lexical-|this|, at all.
Sorry for the echo :(
/be
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Re: Arrow functions and return values
On Thu, Nov 29, 2012 at 7:42 PM, Rick Waldron waldron.r...@gmail.comwrote:
On Thu, Nov 29, 2012 at 9:41 AM, Brendan Eich bren...@mozilla.org wrote:
Kevin Smith wrote:
It's a bit unclear to me how arrow functions react to semicolons,
for example:
var a = (c) = {
var b = 2;
b * c;
}
a(4);
Hmmm... I was under the impression that arrow functions with normal
function bodies do *not* implicitly return anything. Maybe I need to
adjust my spec goggles, but I don't see that in the latest draft.
Oh (and d'oh!) you are quite right. There's no implicit return or other
TCP aspect save lexical-|this|, at all.
Oh, I hadn't realized this! In that case, great!
Cheers,
Jussi
Sorry for the echo :(
/be
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