Proposed D2 Feature: => for anonymous delegates

[Don]

Andrei Alexandrescu wrote:
> Don wrote:
>> Andrei Alexandrescu wrote:
>>> language_fan wrote:
>>>> 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.
>>>
>>> The program should be roughly equivalent with:
>>>
>>> int f(int delegate(int) g) {
>>>     return g(13);
>>> }
>>>
>>> auto __fun(T)(T x) { return x+13; }
>>>
>>> void main() {
>>>     f(&__fun);
>>> }
>>>
>>> which fails with
>>>
>>> Internal error: e2ir.c 644
>>>
>>> :o)
>>
>> Can't reproduce that. It doesn't ICE for me. Tried on several DMD 
>> versions. (Doesn't compile, though).
> 
> Sorry, it's the emacs paste buffer being different from Thunderbird's 
> that's the problem. Please try this.
> 
> int f(int delegate(int) g) {
>     return g(13);
> }
> 
> void main() {
>     auto __fun(T)(T x) { return x+13; }
>     f(cast(int delegate(int)) __fun);
> }
> 
> On my machine:
> 
> __fun(T)
> Internal error: e2ir.c 644

Yup. I've created bug 3432 with a reduced test case.