Nested function requires forward declaration?

[Mike Parker]

On Thursday, 14 April 2022 at 08:55:25 UTC, Chris Katko wrote:

> I imagine this is a really odd edge case but it's piqued my 
> interest.

Consider this:

```d
void main() {
     void foo() { initRuntimeState(i); }
     foo();
     if(!modifyRutimeState()) return;
     int i = getRandomValue();
     i = returnSomethingBasedOnRuntimeState(i);
}
```

Which value of `i` should `foo` use? What if `modifyRuntimeState` 
and `returnSomethingBasedOnRuntimeState` are dependent on 
`initRuntimeState`?

At module scope, and in class/struct declarations, only 
compile-time values can be used to initialize variables and 
assignment is illegal, so the compiler can jump around 
initializing things in any order it wants. It has a well-defined 
and limited set of rules it can work with.

That just isn't the case in local scopes, where a variable's 
lifetime begins at the point of declaration, the scope can exit 
at any time, and the order of evaluation can have side effects 
that change the run-time state.