Daniel Keep wrote:
...
I see that neither the constructor nor the postblit is called.
Apparently the bit representation is used. This has the risk of
violating struct invariants.
Is it legal?
Thank you,
Ali
cast is to value conversions what a tactical nuclear strike is to
peaceful negotiations. cast is specifically *designed* to circumvent
the type system's protections [1].
If you want to do a value conversion, *do a value conversion*. Allocate
a new array and convert each member. cast doesn't call the constructor
or the postblit because it's doing a pointer conversion.
Your code is basically equivalent to this:
void main()
{
auto tmp = "hello"d;
auto mine = cast(MyChar*)(tmp.ptr)
[0..(tmp.length*typeof(tmp[0]).sizeof)/MyChar.sizeof)];
}
That is, it's doing an unsafe, unchecked pointer cast, then re-slicing
the array.
There is another gotcha to watch out for: Array literals are treated
differently from other arrays. That is, the compiler does a value
conversion for literals.
import std.stdio;
void main()
{
auto a = [1, 2, 3];
auto b = cast(float[]) a;
auto c = cast(float[]) [1, 2, 3];
writeln(a); // Prints "1 2 3"
writeln(b); // Prints "1.4013e-45 2.8026e-45 4.2039e-45"
writeln(c); // Prints "1 2 3"
}
-Lars
