On Wednesday, 6 February 2013 at 18:15:53 UTC, Dan wrote:
Start with:
struct X {
char c[];
}
Assume you want value semantics - postblit provides this
capability. It appears with 2.061 'this(this) const' is now
supported. Previously, only 'this(this)' was recognized (i.e.
called) when expected. To get value semantics a developer must
choose between these two and for this case the goal is to
ensure 'c = c.dup;' so value semantics are preserved.
Case 1: Go with 'this(this) { c = c.dup; }'. This works just
fine except for the case where you want a const(X) as a member
of some other class. For example: struct Y { const(X) x; }.
Case 2: Go with 'this(this) const { c = c.dup; }'. This is not
possible because you can not change 'c' since the function is
const. Maxim Fomin pointed out a workaround.
Both are bugs, as const constructor are supposed to be able to
set const variable once. See TDPL for reference on that.
struct X {
char c[];
void _postblit_() { c = c.dup; }
this(this) const {
void delegate() dg = &_postblit_;
dg();
}
}
This is also a bug as transitivity of const isn't respected.
Welcome in weirdland !
