Non-Purity of Algebraic opEquals

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On Friday, 18 September 2015 at 13:53:52 UTC, Nordlöw wrote:
> On Friday, 18 September 2015 at 13:22:14 UTC, Nordlöw wrote:
>> Ideas anyone?
>
> I tried tagging up `VariantN` with pure until I got to
>
>     @property inout(T)* peek(T)() inout pure
>     {
>         static if (!is(T == void))
>             static assert(allowed!(T), "Cannot store a " ~ 
> T.stringof
>                     ~ " in a " ~ VariantN.stringof);
>         if (type != typeid(T))
>             return null;
>         static if (T.sizeof <= size)
>             return cast(inout T*)&store;
>         else
>             return *cast(inout T**)&store;
>     }
>
> which then errors as
>
> variant.d(701,13): Error: pure function 
> 'std.variant.VariantN!32LU.VariantN.peek!void.peek' cannot call 
> impure function 'object.opEquals'
>
> for the line
>
>     if (type != typeid(T))
>
> Why is `object.opEquals` not pure?

It's a long story, but it boils down to the simple fact that 
nobody's gotten around to it yet. I think the plan was to make it 
templated, but Jonathan Davis knows more about it than anyone.