Alignments in std.variant.Algebraic

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bearophile_hugs reported this on 2011-09-29T11:07:53Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=6742

CC List

• andrei (@andralex)
• andy
• bugzilla (@WalterBright)
• lovelydear

Description

In DMD 2.056head std.variant.Algebraic seems to ignore alignment requirements:


import std.variant: Algebraic;
static assert(double.alignof == 8);
struct Foo { double x; }
alias Algebraic!(Foo) AFoo1;
static assert(AFoo1.sizeof == 12);
struct AFoo2 {
    bool b;
    double x;
}
static assert(AFoo2.sizeof == 16);
void main() {}

[dlangBugzillaToGithub]

lovelydear commented on 2012-04-27T15:05:18Z

Compiles and runs on 2.059 Win32

[dlangBugzillaToGithub]

bearophile_hugs commented on 2012-05-22T15:22:50Z

(In reply to comment #1)
> Compiles and runs on 2.059 Win32

That's the problem. I think AFoo1.sizeof has to be 16 byte, to respect the algnment of doubles that is 8.

[dlangBugzillaToGithub]

andy commented on 2015-01-30T02:40:46Z

In DMD 2.066.1, I get:


import std.variant: Algebraic;
static assert(double.alignof == 8); //  Error here, this should be 4.

struct Foo { double x; }
alias Algebraic!(Foo) AFoo1;
static assert(AFoo1.sizeof == 12);
struct AFoo2 {
    bool b;
    double x;
}
static assert(AFoo2.sizeof == 16);  // Error here, it should be 12.
void main() {}

I'm not sure what that means though.

[dlangBugzillaToGithub]

bugzilla (@WalterBright) commented on 2019-12-03T10:14:21Z

On linux, the current compile reports 8 / 16 / 16. As far as I understand this, this is correct. Did not test windows though.