Perfect forwarding

[Jean-Louis Leroy]

On Thursday, 30 July 2020 at 04:56:55 UTC, Petar Kirov 
[ZombineDev] wrote:

> For example:
>
> R fun(
>   scope P1 arg1,
>   return int* arg2,
>   lazy @intetval(-16, 320) long arg3,
>   @interval(0, 127) uint arg4,
>   ref @interval(0, 8192) size_t arg5
> );
>
> The task is create a template, which given a function type like 
> typeof(&fun) returns a new function type with all integer 
> parameters replaced by the smallest type that is big enough to 
> hold the interval specified by the UDA and preserves all 
> storage classes.
>
>
> R hun(
>   scope P1 arg1,
>   return int* arg2,
>   lazy @intetval(-16, 320) short arg3,
>   @interval(0, 127) ubyte arg4,
>   ref @interval(0, 8192) ushort arg5
> );
>
> The way I'd like to go about solving this is like this:
>
> template TightenIntegerParams(Fun)
> {
>   alias TightenIntegerParams =
>     ReturnType!Fun function(
>       staticMap!(
>         TightenParam,
>         Parameters!Fun
>       )
>     );
> }
>
> However the moment staticMap internally does `Args[i]` in order 
> to pass the i-th element to the mapping function `F` we lose 
> all information about the storage classes and UDAs.

Yes I know. My original problem was:

// from
@attrs ref int foo(@otherattrs virtual!Foo obj1, lazy int var, 
ref virtual!Bar obj2);

// make:
@attrs ref int foo(@otherattrs Foo obj1, lazy int var, ref Bar 
obj2) {
     return dispatch(obj1, obj2)(obj1, var, obj2);
}

Back to what you described, is it a real use case? I am thinking 
of writing an article on function generation for the D blog. I 
was wondering how often this sort of transformation is needed.