Re: 'this' in base class out contract

[bearophile]

Michael Shulman:

> Why does the following code fail the assertion?

I don't know the answer yet, but I suggest to generally compile your D code 
with the -w compiler switch.

I have modified the code, the __gshared and the assert removal are to simplify 
the asm:

import std.c.stdio: printf;

class Klass1 {
    void foo()
        out {
            printf("Klass1.this: %x\n", cast(void*)this);
            printf("Klass1.stored: %x\n", cast(void*)stored);
            //assert(stored is this);
        } body {}
}

__gshared Klass1 stored;

class Klass2 : Klass1 {
    override void foo() {
        printf("Klass2.this: %x\n", cast(void*)this);
        stored = this;
    }
}

void main () {
    Klass2 x = new Klass2();
    printf("x: %x\n", cast(void*)x);
    x.foo();
}

Output:
x: 14e2fd0
Klass2.this: 14e2fd0
Klass1.this: 41d1b0
Klass1.stored: 14e2fd0

I have compiled it with (dmd 2.053):
dmd -O


The asm:

_D4test6Klass13fooMFZv  comdat
L0:             push    EBP
                mov     EBP,ESP
                sub     ESP,018h
                mov     -018h[EBP],EAX
                call    near ptr _D9invariant12_d_invariantFC6ObjectZv
                lea     EAX,-018h[EBP]
                call    near ptr _D4test6Klass13fooMFZv8__ensureMFZv
                mov     ESP,EBP
                pop     EBP
                ret

_D4test6Klass13fooMFZv8__ensureMFZv     comdat
L0:             push    EAX
                mov     ECX,offset FLAT:_DATA
                push    dword ptr [EAX]
                push    ECX
                call    near ptr _printf
                mov     EAX,offset FLAT:_DATA[014h]
                push    dword ptr _D4test6storedC4test6Klass1
                push    EAX
                call    near ptr _printf
                add     ESP,010h
                pop     EAX
                ret

_D4test6Klass23fooMFZv  comdat
L0:             push    EBP
                mov     EBP,ESP
                sub     ESP,014h
                push    EBX
                mov     EBX,EAX
                call    near ptr _D9invariant12_d_invariantFC6ObjectZv
                mov     EAX,offset FLAT:_D4test6Klass16__vtblZ[01Ch]
                push    EBX
                push    EAX
                call    near ptr _printf
                mov     EAX,EBX
                mov     _D4test6storedC4test6Klass1,EBX
                call    near ptr _D4test6Klass13fooMFZv8__ensureMFZv
                add     ESP,8
                pop     EBX
                mov     ESP,EBP
                pop     EBP
                ret

__Dmain comdat
L0:             push    EBX
                mov     EAX,offset FLAT:_D4test6Klass27__ClassZ
                push    EAX
                call    near ptr __d_newclass
                add     ESP,4
                mov     ECX,offset FLAT:_D4test6Klass26__vtblZ[01Ch]
                push    EAX
                mov     EBX,EAX
                push    ECX
                call    near ptr _printf
                mov     EDX,[EBX]
                mov     EAX,EBX
                call    dword ptr 018h[EDX]
                add     ESP,8
                xor     EAX,EAX
                pop     EBX
                ret

Bye,
bearophile