On 04/06/2011 05:13 PM, bearophile wrote:
> Given an array of strings std.string.join() returns a single string:
>
> import std.string;
> void main() {
> string[] a1 = ["hello", "red"];
> string j1 = join(a1, " "); // OK
> }
>
>
> But in a program I need an array of mutable arrays of chars. If I
join the arrays I get a mutable array of chars. But I need a string:
Tangentially off-topic: This does not apply to your case, but I think we
should think twice before deciding that we need a string. For example,
functions parameters should be const(char[]) (or const(char)[]) instead
of string as that type accepts both mutable and immutable strings.
>
> import std.string;
> void main() {
> char[][] a2 = ["hello".dup, "red".dup];
> string j2 = join(a2, " "); // error
If possible, this might work:
const(char[]) j2 = join(a2, " ");
There is also std.exception.assumeUnique, but it's too eager to be safe
and tries to null its parameter and this fails:
string j2 = assumeUnique(join(a2, " ")); // error
Finally, casting ourselves works:
string j2 = cast(string)join(a2, " ");
> }
>
> Error: cannot implicitly convert expression (join(a," ")) of type
char[] to string
>
> ..idup avoids the error:
>
> string j3 = join(a2, " ").idup; // OK
>
> Given the low efficiency of the D GC it's better to reduce memory
allocations as much as possible.
> Here join() creates a brand new array, so idup performs a useless
copy. To avoid this extra copy do I have to write another joinString()
function?
>
> Bye,
> bearophile
Ali
