Is this a bug? +goto

[Stanislav Blinov]

On Monday, 5 November 2018 at 23:54:59 UTC, MatheusBN wrote:
> Hi,
>
> I posted this in another thread but without any response.
>
> This code:
>
> void main(){
>      goto Q;
>      int x;
>      Q:
>      writeln("a");
> }
>
> Gives me this error: "source_file.d(4): Error: goto skips 
> declaration of variable source.main.x at source_file.d(5)"
>
>
> Now, if I add a pair of brackets:
>
> void main(){
>      {
>          goto Q;
>          int x;
>      }
>      Q:
>      writeln("a");
> }
>
> It works. So Is this a bug?


No, it's not. Consider replacing that int with a type that has a 
destructor:

struct S { ~this() { /* ... */ } }

void main(){
      goto Q;
      S x;
      Q:
      writeln("a");
} // <---

Now, what should happen at that closing paren is a destructor 
call, x.__dtor. However, goto jumps over initialization of 'x', 
which would lead to calling a destructor on an uninitialized 
value. That's why the compiler disallows such skips.

But here it's fine:

void main(){
      {
          goto Q;
          S x;
      } // <---
      Q:
      writeln("a");
}

because goto jumps over both initialization *and* destruction, 
i.e. neither would even be performed.

I'm guessing you misunderstood the author of that other thread. 
What he's saying is that code similar to the *second* version 
fails. That's what all the commotion is about over there. This 
simple example obviously works, yet in his more complicated code 
base something goes wrong.