Infer return type from assignment

[ixid]

On Wednesday, 11 April 2018 at 14:33:06 UTC, Adam D. Ruppe wrote:
> On Wednesday, 11 April 2018 at 14:26:53 UTC, ixid wrote:
>> Is it possible to infer a template's return type from what 
>> it's assigned to? If not is this a difficult or worthless 
>> feature to add?
>
> Not really. The function call needs to make sense by itself:
>
> fun(a)
>
> needs to be a complete thing for a lot of things in the 
> language to work. Type checking assumes it is there, inference 
> assumes it is there, overloading assumes it s there, etc.
>
> void foo(int);
> void foo(float);
>
> foo(fun(a)); // what happens?
>
>
> So I don't say anything is impossible that isn't a paradox... 
> but the effort level to solve all these problems would be 
> really high for D.

I am sure there are all sorts of thorns involved but for your 
example a somewhat arbitrarily defined fallback hierarchy of 
types from most complex to most simple, with it matching the most 
'simple' that it can.