Union of same type in C++

Question

Whenever I see examples of union, they are always different types. For example, from MSDN:

// declaring_a_union.cpp
union DATATYPE    // Declare union type
{         


        

Answer 1

This is legal and very useful in situations where you have different contexts, where different names would be more appropriate. Take a four member vector vec4 type for example (similar to what you'd find in GLSL):

vec4 v(1., 1., 1., 1.);

// 1. Access as spatial coordinates
v.x;
v.y;
v.z;
v.w;

// 2. Access as color coordinates (red, green, blue, alpha)
v.r;
v.g;
v.b; 
v.a;

// 3 Access as texture coordinates
v.s;
v.t;
v.p;
v.q;

A vec4 may only have four members of the same type, but you'd use different names to refer to the same objects, depending on the context.