Perfect forwarding

[Manu]

On Thu, Jul 30, 2020 at 3:45 PM Petar via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> On Thursday, 30 July 2020 at 04:56:55 UTC, Petar Kirov
> [ZombineDev] wrote:
> > On Wednesday, 29 July 2020 at 16:31:08 UTC, Jean-Louis Leroy
> > wrote:
> >> [...]
> >
> > My point, that you can't do much useful processing with
> > `__parameters` (except pass all of subset of it), still stands.
> >
> > Say you have a function with N parameters. Some of those
> > parameters are integers and may have a UDA attached to them
> > that specifies the minimum and maximum value they may receive.
> > 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.
>
> I now saw that Manu clarified what he meant.
>
> Also I do realize that what we actually need is for
> `Parameters!fun[0]` to return a parameter object that includes
> not just the type but also the parameter name, UDAs attached and
> storage classes. If for example `ref` was a type qualifier, or
> just otherwise preserved by `alias`-ing it would help, but not
> solve the whole issue.
>

UDA's and default args are in-language concepts, alias/tuples can handle
them, and don't require any particularly special meta to handle.
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