Tried using DtoDeclarationExp for VarDecls in Statements to fix nesting issues (see bug #104), but a separate helper that doesn't initialize would be nicer.

module union1;

union U
{
    float f;
    int i;
}

void main()
{
    float f = 2;
    U u = U(f);
    assert(u.i == *cast(int*)&f);
}