Mixin helper help

TheZipCreator thezipcreator at protonmail.com
Sat Jan 14 23:07:13 UTC 2023


On Thursday, 12 January 2023 at 08:03:34 UTC, John Chapman wrote:
> I'm obviously doing something wrong, but don't quite understand.
>
> ```d
> mixin template helper() {
>   mixin("writeln(12);");
> }
>
> struct Foo {
>   void opDispatch(string name)() {
>     import std.stdio;
>     mixin helper!();
>     //mixin("writeln(12);");
>   }
> }
>
> void main() {
>   Foo.init.opDispatch!"bar"();
> }
> ```
>
> The compiler emits these errors about the mixin 
> ("writeln(12);"):
> unexpected `(` in declarator
> basic type expected, not `12`
> found `12` when expecting `)`
> no identifier for declarator `writeln(_error_)`
> semicolon expected following function declaration
> declaration expected, not `)`
>
> Why does the commented code work but the mixin not? Thanks for 
> any pointers.

This is not the purpose mixin templates are meant to serve. 
They're for copying declarations into scopes (and as such only 
support declarations in them). Instead, I think what you want is
```d
template helper() {
	const char[] helper = `writeln(12);`;
}

struct Foo {
	void opDispatch(string name)() {
		import std.stdio;
		mixin(helper!());
	}
}

void main() {
	Foo.init.opDispatch!"bar"();
}
```


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