On Tuesday, 16 February 2016 at 09:39:31 UTC, Sönke Ludwig wrote:
Am 16.02.2016 um 08:20 schrieb Ola Fosheim Grøstad:
On Monday, 15 February 2016 at 22:48:16 UTC, Walter Bright
wrote:
rears its head again :-)
Head Const is what C++ has for const, i.e. it is not
transitive,
applies to one level only. D has transitive const.
What head const will do for us:
1. make it easy to interface to C++ code that uses const, as
currently
it is not very practical to do so, you have to resort to
pragma(mangle)
2. supports single assignment style of programming, even if
the data
is otherwise mutable
The downside is, of course, language complexity.
Maybe you can get away with adding "mutable", which is needed
for
intrusive ref counting as well:
C++:
Type * const ptr;
struct ConstType {
mutable int rc;
}
D:
const mutable(Type)* ptr;
struct ConstType {
mutable(int) rc;
}
As a bonus, this would also provide a natural syntax to define
tail-const class references:
mutable const(C) something;
Another bonus to introducing the mutable keyword is the option to
make everything immutable by default (in a future version of D)
and allow the users to have mutable objects only if they use the
mutable keyword.
