Debug help - delegate from dlang Tour

[evilrat]

On Monday, 8 September 2025 at 14:32:32 UTC, Brother Bill wrote:
> https://tour.dlang.org/tour/en/basics/delegates
>
> This is so simple.  What is D complaining about?
> Should this also work with a Template, as shown?
>
> ```
> import std.stdio;
>
> void main()
> {
> 	// auto add(T)(T lhs, T rhs)
> 	// {
> 	// 	return lhs + rhs;
> 	// }
>
> 	int add(int lhs, int rhs) {
> 		return lhs + rhs;
> 	}
>
> 	int doSomething(int function(int, int) doer)
> 	{
> 		// call passed function
> 		return doer(5, 6);
> 	}
>
> 	doSomething(&add);
>
> }
>
> ```
>
> Console output:
> ```
> c:\dev\D\D_templates_tutorial\toy1\source\app.d(20): Error: 
> function `doSomething` is not callable using argument types 
> `(int delegate(int lhs, int rhs) pure nothrow @nogc @safe)`
>     doSomething(&add);
>                ^
> c:\dev\D\D_templates_tutorial\toy1\source\app.d(20):        
> cannot pass argument `&add` of type `int delegate(int lhs, int 
> rhs) pure nothrow @nogc @safe` to parameter `int function(int, 
> int) doer`
> c:\dev\D\D_templates_tutorial\toy1\source\app.d(14):        
> `app.main.doSomething(int function(int, int) doer)` declared 
> here
>     int doSomething(int function(int, int) doer)
>         ^
> ```

probably because you have declared nested function `add` inside 
`main`, this creates a delegate closure capturing `main` scope, 
if you don't want that just mark `add` static.