If both LHS & RHS are equal swizzle type a full assignment is made

[Sairony]

swizzle::glsl::naive::vector< float, 4 > lhs, rhs( 1.0f, 1.0f, 1.0f, 1.0f ); lhs.xy = rhs.xy; // lhs becomes 1,1,1,1 when expected to be 1,1,0,0

[gwiazdorrr]

This is the intended behaviour.