std.typecons.Rebindable!(immutable A) is implemented as:
private union {
immutable(A) original;
A stripped;
}
...@trusted assignment operators...
@property inout(immutable(A)) get() @trusted pure nothrow
@nogc inout
{
return original;
}
alias get this;
This conforms with the D safety spec: All access to the unsafe
union goes through the @trusted get() and the trusted assignment
operators.
Rebindable!(immutable A) r = a1;
// r.original is a1
r = a2;
// r.original is a2
But the compiler may assume that immutable variables -- such as
the immutable(A) original -- never change and thus may optimize
code. Since immutable(A) original is assignable in the union,
such optimization would produce wrong behavior: In the final
line, the compiler could think that r.original is a1 without
examining r.original.
How does Rebindable prevent the compiler from optimizing
according to immutable's rules?
