"ubyte[size] store = void" in std.variant

[Graham Fawcett]

On Tue, 15 Jun 2010 10:29:56 -0400, Steven Schveighoffer wrote:

> On Tue, 15 Jun 2010 09:04:23 -0400, Graham Fawcett <fawcett at uwindsor.ca>
> wrote:
> 
>> Hi folks,
>>
>> The following statement appears in std.variant:
>>
>> 190    union
>> 191    {
>> 192        ubyte[size] store = void;
>> 193        // conservatively mark the region as pointers 194       
>> static if (size >= (void*).sizeof) 195            void* p[size /
>> (void*).sizeof]; 196    }
>>
>> The '= void' on line 192 sometimes leads to 'Error: void initializer
>> has no value' errors in application code. For example, this fails to
>> compile on DMD 2.047:
>>
>>   foreach (int v; map! "a.get!int" (variantArray(1,2,3)))
>>     writeln(v);
>>
>> Changing line 192 to 'ubyte[size] store;' resolves the issue.
>>
>> My question is: what is the point of the '= void' initializer here?
>> Would std.variant be broken if '= void' were removed?
> 
> = void means don't initialize the data.  Otherwise, the compiler/runtime
> will fill in the data will all 0s.  However, I'm not sure how that works
> with a union, since you may have conflicting requirements for
> initialization.

I'm not sure if it's in the spec, but a quick test results in a
compiler error if I declare a union with overlapping initializers.

Simplifying the 'std.variant' case, I get the same 'void initializer
has no value' error like this:

    struct foo {
      ubyte[] store = void;
    }
    foo z = foo();

Is this a compiler bug?

Graham