Proposed D2 Feature: => for anonymous delegates

[language_fan]

Wed, 21 Oct 2009 12:35:41 +0200, Pelle Månsson thusly wrote:

> Andrei Alexandrescu wrote:
>> Pelle Månsson wrote:
>>> Jason House wrote:
>>>> Andrei Alexandrescu Wrote:
>>>>
>>>>> Jason House wrote:
>>>>>> Am I the only one that has trouble remembering how to write an
>>>>>> inline anonymous delegate when calling a function? At a minimum,
>>>>>> both Scala and C# use (args) => { body; } syntax. Can we please
>>>>>> sneak it into D2?
>>>>> We have (args) { body; }
>>>>>
>>>>> Andrei
>>>>
>>>> Somehow, I missed that. What kind of type inference, if any, is
>>>> allowed? Scala and C# allow omiting the type. Lately I'm doing a lot
>>>> of (x) => { return x.foo(7); } in C# and it's nice to omit the
>>>> amazingly long type for x. The IDE even knows the type of x for
>>>> intellisense... I think scala would allow x => foo(7), or maybe even
>>>> => _.foo(7) or even _.foo(7). I haven't written much scala, so I may
>>>> be way off...
>>>
>>> Recent experiments by myself indicate you cannot omit the type and you
>>> cannot use auto for the type, so you actually need to type your
>>> VeryLongClassName!(With, Templates) if you need it.
>>>
>>> I sort of miss automatic type deduction.
>> 
>> Actually, full type deduction should be in vigor, but it is known that
>> the feature has more than a few bugs. Feel free to report any instance
>> in which type deduction does not work in bugzilla.
>> 
>> Andrei
> 
> int f(int delegate(int) g) {
>      return g(13);
> }
> void main() {
>      f((auto x) { return x+13; });
> }
> 
> This does not compile in D v2.034. Am I missing something?

No, in this context the exact type can be inferred unambiguously without 
worrying about overloading. From the error message

test.d(5): basic type expected, not auto
test.d(5): found 'auto' when expecting ')'
test.d(5): semicolon expected following function declaration
test.d(5): found 'x' when expecting ','
test.d(5): expression expected, not ')'
test.d(5): found '{' when expecting ','
test.d(5): expression expected, not 'return'
test.d(5): found 'x' when expecting ','
test.d(5): found ';' when expecting ','
test.d(5): expression expected, not '}'

I can see that the compiler does not even support this on syntactic level.