Question

How can I provide a class that has constructors as part of a union?

I’ve read that any class that has a trivial constructor can be part of a union. Especially with c++0x, I thought unions are supposed to be unrestricted. Why is this float4 class not suitable? How can I do this?

struct float4
{
    union
    {
        struct { float z, y, x, w; };
        float v[4];
        __m128 xmm;
    };

    inline float4() { }
    inline float4(float x, float y, float z, float w) :
        xmm(_mm_setr_ps(z, y, x, w)) { }
};

struct float44
{
    union
    {
        float v[16];
        __m128 xmm[4];
        struct { __m128 xmm1, xmm2, xmm3, xmm4; };
        struct { float4 row1, row2, row3, row4; };
    };
};

Answer 1

VC2010 doesn’t implement that part of the C++0x spec yet.