Chars sorting and copies

[Steven Schveighoffer]

On Sat, 22 Oct 2011 23:01:17 -0400, bearophile <bearophileHUGS at lycos.com>  
wrote:

> Thanks for all the answers.
>
> Steven Schveighoffer:
>
>> a ~ b should technically be assignable to char[], since it's alread new
>> memory.  We may yet get there with pure functions being able to implicit
>> cast to immutable.
>
> Isn't that kind of the opposite?

No, if a ~ b would call a pure function that returns mutable when  
possible, then you could use it for mutable, immutable, or const.

> Is this already in Bugzilla?

Somewhat, although I like using the pure function avenue to ensure  
immutable does not violate const than the crazy rules we came up with here:
http://d.puremagic.com/issues/show_bug.cgi?id=1654

Note this was in the infancy of my D knowledge ;)

> Some versions I have written, there is no very good solution, it seems:
>
>
> import std.algorithm, std.exception;
>
> void main() {
>     string a = "red";
>     string b = "green";
>     int[string] aa;
>
>     // Works in D1.
>     // aa[(a ~ b).sort] = 1;
>
>     // Works in D2, but will stop working.
>     aa[(a.dup ~ b.dup).sort.idup] = 1;
>
>     // Works in D2, but will stop working.
>     char[] ab = (a.dup ~ b.dup).sort;
>     aa[assumeUnique(ab)] = 2;
>
>     // If keys don't actually need to be strings
>     // the code gets a bit simpler.
>     int[immutable(ubyte[])] aa2;
>
>     // not good
>     // aa2[assumeUnique(sort(cast(ubyte[])(a ~ b)))] = 3;
>
>     // not good?
>     // aa2[assumeUnique(sort(cast(ubyte[])(a ~ b)).release())] = 3;
>
>     // just 1 copy, two visible casts, 3 lines
>     auto ab4 = cast(ubyte[])(a ~ b);
>     ab4.sort();
>     aa2[cast(immutable(ubyte[]))ab4] = 3;
>
>     // a visible cast and an hidden cast
>     ubyte[] ab2 = cast(ubyte[])(a ~ b);
>     ab2.sort();
>     aa2[assumeUnique(ab2)] = 3;
>
>     // 2 lines, more complex looking
>     auto ab3 = sort(cast(ubyte[])(a ~ b)).release();
>     aa2[assumeUnique(ab3)] = 3;
> }

I honestly am not sure your specific problem is solvable without a lot of  
special cases.  It may be you have to write a sub-function that hides the  
mess.

-Steve