$ dmd --version
DMD64 D Compiler v2.068
Copyright (c) 1999-2015 by Digital Mars written by Walter Bright
$ cat app.d 
import core.internal.hash;

struct Foo {
    int[] arr;
    alias arr this;
}

void main() {
    Foo().hashOf();
}
$ dmd app.d 
app.d(9): Error: core.internal.hash.hashOf called with argument types (Foo) matches both:
/usr/include/dlang/dmd/core/internal/hash.d(40):     core.internal.hash.hashOf!(Foo).hashOf(Foo val, ulong seed)
and:
/usr/include/dlang/dmd/core/internal/hash.d(112):     core.internal.hash.hashOf!(Foo).hashOf(Foo val, ulong seed)
/usr/include/dlang/dmd/object.d(2999): Error: core.internal.hash.hashOf called with argument types (Foo, ulong) matches both:
/usr/include/dlang/dmd/core/internal/hash.d(40):     core.internal.hash.hashOf!(Foo).hashOf(ref Foo val, ulong seed)
and:
/usr/include/dlang/dmd/core/internal/hash.d(112):     core.internal.hash.hashOf!(Foo).hashOf(ref Foo val, ulong seed)
app.d(9): Error: template instance object.hashOf!(Foo) error instantiating