Parameters declared as the alias of a template won't accept the arguments of the same type.
Elfstone
elfstone at yeah.net
Tue May 3 06:20:53 UTC 2022
On Monday, 2 May 2022 at 16:29:05 UTC, Loara wrote:
> On Sunday, 1 May 2022 at 03:57:12 UTC, Elfstone wrote:
>> [...]
>
> Template deduction for aliased function parameter is a very
> tricky argument and it's not so simple to handle in certain
> cases. Consider for example this code:
>
> ```d
> template MyAlias(T){
> alias MyAlias = int;
> }
>
> T simp(T)(MyAlias!T val){
> return T.init;
> }
>
> int main(){
> simp(3);//Impossible to deduce T
> simp( cast(MyAlias!string) 4);//Also invalid since
> MyAlias!string is exactly int
> simp!string(4);//Ok, no parameter deduction
> }
> ```
>
> Instead to use aliases it's better (both in D and in C++) to
> use constraints/concepts.
Yeah, I understand some cases are impossible, and to be avoided.
I believe your example is also impossible in C++, but it's better
the compiler do its job when it's totally possible - needless to
say, C++ compilers can deduce my _dot_.
Constraints/Concepts are useful, but what's needed here is a
literal _alias_. There's no ambiguity, no extra template
parameters introduced in the declaration.
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