Why I (Still) Won't Use D

[Janice Caron]

On 28/03/2008, Walter Bright <newshound1 at digitalmars.com> wrote:
> Making strings arrays of invariant makes them implicitly copy-on-write.

We're drifting off topic here, but ... I don't think that's right.

Example:

    string s = "hello";
    string t = std.string.replace(s,"x","y");
    assert(s == t); // OK
    assert(s is t); // *FAILS*

This example demonstrates that std.string.replace() does not do
copy-on-write. (Instead, it does copy-always). Thus, as I was saying,
whether or not copy-on-write is done is part of the algorithm, not
part of the type. Of course, std.string.replace() could be rewritten
to implement copy-on-write, but that would kinda prove my point.
Invariant arrays make copy-on-write /possible/, but they don't make it
mandatory.


>  More generally, whether D arrays are copy-on-write or not is based on
>  whether the element type is invariant or mutable.

Again, it is /possible/ to implement copy-on-write using mutable
strings (as MSVC++ std::string proves) - just very difficult. But D's
immutable makes it easy.


> It isn't based on if
> the contents are text or not.

No argument there! :-)