Return type deduction

[Lodovico Giaretta via Digitalmars-d]

On Monday, 5 September 2016 at 09:59:16 UTC, Andrea Fontana wrote:
> I asked this some time (years?) ago. Time for a second try :)
>
> Consider this:
>
> ---
>
> T simple(T)() { return T.init; }
>
>
> void main()
> {
> 	int test = simple!int(); // it compiles
> 	int test2 = simple();    // it doesn't
> }
>
> ---
>
> Is there any chance to implement this kind of deduction?
> Please notice that it doesn't break any existing code, I guess.
>
> For example using my json wrapper [1] this sounds a bit 
> pedantic:
>
> ----
> user.name = json.get!string("info/name");
> user.age  = json.get!int("info/age");
> ----
>
> If return type deduction could be implemented it would be:
>
> ----
> user.name = json.get("info/name");
> user.age  = json.get("info/age");
> ----
>
> [1] https://code.dlang.org/packages/jsonwrap
>
> Andrea

I see just one problem in this request:

===========================
T get(T = int)()
{
     return T.init;
}

double val = get(); // should this call get!double or try to call 
get!int and give an error?
===========================

That is, what takes precedence? Default argument or inference 
from the destination type? I'd personally prefer this to give an 
error, as it is ambiguous and error prone.