Nick Sabalausky wrote:
"Jeremie Pelletier" <jerem...@gmail.com> wrote in message
news:h9mmre$1i8...@digitalmars.com...
Ary Borenszweig wrote:
Object is not-nullable, Object? (or whatever syntax you like) is
nullable. So that line is a compile-time error: you can't cast a null to
an Object (because Object *can't* be null).
union A {
Object foo;
Object? bar;
}
Give me a type system, and I will find backdoors :)
Unions are nothing more than an alternate syntax for a reinterpret cast. And
it's an arguably worse syntax because unlike casts, uses of it are
indistinguishable from normal safe code, there's nothing to grep for. As
such, unions should never be considered any more safe than cast(x)y. The
following is just as dangerous as your example above and doesn't even touch
the issue of nullability/non-nulability:
union A {
int foo;
float bar;
}
Yet it's the only way I know of to do bitwise logic on floating points
in D to extract the exponent, sign and mantissa for example.
And yes they are much, much more than a simple reinterpret cast, a
simple set of casts will not set the size of the union to its largest
member. Unions make for elegant types which can have many valid
representations:
union Vec3F {
struct { float x, y, z; }
float[3] v;
}
I just can't picture D without unions :)
