Get the return type of the function

[xtreak via Digitalmars-d-learn]

On Wednesday, 3 February 2016 at 17:40:23 UTC, Meta wrote:
> On Wednesday, 3 February 2016 at 17:12:03 UTC, xtreak wrote:
>> I was reporting a patch for the regression by removing the 
>> code that was causing the error. The bug was that map was not 
>> accepting multiple lambdas. It was suggested to check for void 
>> functions and lambdas. I couldn't find a function to check for 
>> return type in the std.traits. I tried the explicit for loop 
>> thus checking for the void functions as in the else case. I am 
>> D newbie it will be helpful in having the community help me in 
>> fixing the issue.
>>
>> foreach(g, i; fun) {
>>   alias k = unaryFun!(fun[g]);
>>   static assert(!is(AppliedReturnType!k == void), "Mapping 
>> function must not return void.");
>> }
>>
>> Bug report : https://issues.dlang.org/show_bug.cgi?id=15480
>> Seems depends on : 
>> https://issues.dlang.org/show_bug.cgi?id=5710
>> Pull request : 
>> https://github.com/D-Programming-Language/phobos/pull/3963
>> Introduced as a part of 
>> https://github.com/D-Programming-Language/phobos/pull/1917
>
> Unles I'm misunderstanding you, you can get the return type of 
> a function by using std.traits.ReturnType:
>
> void test() {}
> static assert(is(ReturnType!test == void));

Thanks. I was trying to get the return type of lambdas. I was 
trying the following and got an error. I was using dpaste with 
dmd 2.070

writeln(ReturnType!(a =(a *a)))

Error: template instance f662.main.ReturnType!((a) => a * a) does 
not match template declaration ReturnType(func...) if 
(func.length == 1 && isCallable!func)