On Tue, 15 Jun 2010 11:18:07 -0400, Graham Fawcett <[email protected]>
wrote:
On Tue, 15 Jun 2010 10:29:56 -0400, Steven Schveighoffer wrote:
On Tue, 15 Jun 2010 09:04:23 -0400, Graham Fawcett <[email protected]>
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?
Note, you can only use = void on a value type, not a dynamic array. The
variant union member is a static array, not a dynamic one.
But actually, now that I think about it, =void is generally used in a
function, not in a type definition. I'm not sure = void should be allowed
in that context. So maybe the compiler is right to complain...
-Steve
