Wrap a call?

[Nick Treleaven]

On Wednesday, 18 February 2026 at 19:43:38 UTC, JN wrote:
>     template WrapCall(string call)
>     {
>         enum WrapCall = "before(); " ~ call ~ "; after();";
>     }
>
>     void main()
>     {
>         mixin WrapCall!"add(1, 2)";
>     }

The mixin statement inserts the body of the template into main's 
scope, so this just declares a string enum:

```d
void main()
{
     enum WrapCall = "before(); " ~ "add(1, 2)" ~ "; after();";
}
```
Note that eponymous templates don't do anything special for mixin 
statements.

> This doesn't work, if I change it to mixin(WrapCall!"add(1, 
> 2")), it works, why?

Because that string mixin takes an enum string template 
instantiation and parses it as if it were code inside main, so 
you get:

```d
void main()
{
     before(); add(1, 2); after();
}
```