Member function increases size of a struct defined in a function - is this a bug?

[Dennis]

On Tuesday, 11 February 2020 at 11:32:47 UTC, Max Samukha wrote:
> Sorry for the late reply. I agree it is not a big issue. On the 
> other hand, to draw an (probably far-fetched) analogy with C++ 
> structs, I would be surprised if the compiler added a vtable 
> pointer to the struct in the absence of virtual functions.

The thing is, because of D's static introspection and 
order-independent declarations things can get very complicated 
very quick. Here is an example that can be compiled two ways:

```
import std;

void main() {
     string str = "from closure";

     struct S {
         int b;

         string method() {
             static if (S.sizeof > int.sizeof) {
                 return str; // current behavior
             } else {
                 return "constant"; // also a valid option
             }
         }
     }
     writeln(S.init.method);
}

```

Of course you can account for paradoxical cases like this, and 
there are cases where the compiler already does:

```
struct S {
     int a = 3;
     static if (S.sizeof == int.sizeof) {
         int b = 3;
     }
     static if (S.sizeof == int.sizeof) {
         int c = 3;
     }
}
```

> variable onlineapp.S.c cannot be further field because it will 
> change the determined S size

But the takeaway is: even if you make a decision a bit more 
intelligently, it can increase compiler complexity in unexpected 
ways.