Explicit cast to @system?

[tsbockman]

On Saturday, 8 October 2022 at 23:06:13 UTC, Anonymouse wrote:
> I have some nested templated code that takes function pointers. 
> In many cases I pass it functions of identical signatures, 
> except some are `@safe` and others are `@system`. In those 
> cases the templates end up getting instantiated twice. I don't 
> care about the `@safe`-ness and I'd really like to just have 
> them all treated as `@system`, with one instantiation per 
> unique signature.
> ...
> But surely there has to be a better way?

You might be templating more information than necessary. In your 
example `foo` doesn't need to be a template at all:
```D
void foo(void function() @system fun) {
     pragma(msg, typeof(fun).stringof);
}
```
If your real code needs to template the return type and 
parameters of `fun`, for example, consider just templating those 
instead of the whole function pointer type:
```D
void foo(R, P...)(R function(P) @system fun) {
     pragma(msg, typeof(fun).stringof);
}
```
(Things do get awkward with `ref` and `out`, though, because D 
considers them to be part of the function's type rather than part 
of the parameter or return types. `ref` is the bane of my D 
meta-programming existence.)