std.variant holding bigger structs and std.concurrency message limitation

[Idan Arye]

On Saturday, 27 April 2013 at 11:37:38 UTC, Tavi Cacina wrote:
> is it a bug the fact that a Variant may be initialized with a 
> struct bigger than 32 bytes? Even if this does function, it is 
> not consistent because you can not assign such an 'inflated' 
> variant to another one, assertion. This affects the max size of 
> a std.concurrency message (right now it is not specified that 
> such restriction exists)
>
> ---
> import std.variant;
>
> struct S
> {
>   int[9] s;
> }
>
> void main()
> {
>   Variant v1, v2; // maximum size 32 bytes
>   v1 = S(); // works, even if sizeof(S) > 32
>   v2 = v1; // AssertError: target must be non-null
> }
> ---

There used to be a maximum size check for placing things in 
variants, but it was removed back in 2009: 
https://github.com/D-Programming-Language/phobos/commit/0c142994d9b5cb9f379eca28f3a625c749370e4a#L20L189

The way it works now, is that if the size is too big they use a 
reference instead: 
https://github.com/D-Programming-Language/phobos/blob/master/std/variant.d#L544#L555