https://issues.dlang.org/show_bug.cgi?id=20559

          Issue ID: 20559
           Summary: Reference type + alias this + AA + AA.clear causes
                    SEGV
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: major
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: pro.mathias.lang@gmail.com

Test code:
```
import std.stdio;

class Bar
{
    int[string] aa;
    alias aa this;
}

void main ()
{
    scope b = new Bar;
    b["Hello"] = 42;
    b.clear; // SEGV happens here, next line is never reached
    writeln("Oopsie");
}
```

This happens because 'clear' is defined as:
> void clear(T : Value[Key], Value, Key)(T aa)

And the code just blindly casts T to a `struct AA`: https://github.com/dlang/druntime/blob/1049bb806679436103f8174c1f77541d5ad99091/src/object.d#L2167-L2170

--