My preferences: 1, 3, 4, 5, (big void), 2.
I actually like 4 the most but I get that that might not be practical if it
leads to unexpected behaviour.
I can’t think of a scenario where capturing by reference would be helpful in a
single line closure. 5 just adds additional complexity with no additional
benefit IMHO.
Also, in response to Rowan, a Ruby-style syntax should be possible though:
{|param| expr}
Only caveat is that the || would be required if there are no parameters:
{|| expr}
Levi has mentioned this one before. You could even omit the braces here.
Ilija
On 30 May 2017, 19:58 +0200, Levi Morrison <le...@php.net>, wrote:
> Internals,
>
> The previous discussion thread has died down significantly and so I'd
> like to start a new one to refocus. This message has some redundant
> information by design so people don't have to reference the other
> thread so much.
>
> Based on the discussion there are a few different syntax choices
> people liked. Overall it's a feature that people seem to want but
> everyone seems to prefer a different syntax choice.
>
> 1. fn(params) => expr
> 2. function(params) => expr
>
> 3. (params) ==> expr
> 4. (params) => expr
>
> Note that 3 and 4 require a more powerful grammar and parser and that
> 4 has ambiguities. I think we can work around them by rules -- only
> mentioning it because its popular because of JavaScript and do not
> prefer this at all.
>
> Note that 1 requires a new keyword.
>
> Option 2 looks the best from that perspective but is by far the
> longest; remember people are partially interested in this feature
> because they want shorter closures which this doesn't really help.
>
> This is why everyone is so divisive. All options have drawbacks.
> Additionally some people don't like binding by value and would prefer
> ref, and others really would be against by-ref.
>
> Which brings me to an option I don't think was ever discussed on list:
>
> 5.
> [](params) => expr // binds no values
> [=](params) => expr // binds by value
> [&](params) => expr // binds by reference
>
> It has quite a few good qualities:
>
> - No new keywords
> - Can choose between reference and value
> - Concise
> - Has precedence in C++, a major language
> - Can be done in our existing grammar and parser[1]
> - Can be extended to allow explicit binding of variables:
> // all equivalent
> // y is bound by value, array by reference
> [&, $y]($x) => $array[] = $x + $y
> [=, &$array]($x) => $array[] = $x + $y
>
> And of course it does have downsides:
>
> - Symbol soup (it uses a lot of symbols)
> - A minor BC break. Empty arrays which are invoked as functions are
> currently guaranteed to be errors at runtime and would have a new
> valid meaning. Here's an example from inside an array literal:
>
> // error at runtime previously
> [ []($x) => $x ]
> // now an array with one item which is a closure that returns
> its parameter
>
> Sara pointed out that we'd need to keep a leading `=` or `&` in the
> array to disambiguate from our array closure form.
>
> Overall I'd prefer 1 or 5. What do you guys think?
>
>
> [1]: I'm pretty sure it can be done but until it's done I can't say
> so confidently because sometimes there are things lurking in our
> grammar I forget about.
>
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