How to reverse char[]?

[James Miller]

> On 02/08/2012 02:29 AM, H. S. Teoh wrote:
>>
>> Hi all,
>>
>> I'm trying to reverse a character array. Why doesn't the following work?
>>
>>        import std.algorithm;
>>        void main() {
>>                char[] array = ['a', 'b', 'c'];
>>                reverse(array);
>>        }
>>
>> I get:
>>
>> Error: template std.algorithm.reverse(Range) if
>> (isBidirectionalRange!(Range)&&  hasSwappableElements!(Range)) does not
>> match any function template declaration
>> Error: template std.algorithm.reverse(Range) if
>> (isBidirectionalRange!(Range)&&  hasSwappableElements!(Range)) cannot deduce
>> template function from argument types !()(char[])
>>
>>
>> T
>>
>
> char[] is handled by Phobos as a range of dchar, ergo it does not have
> swappable elements. Apparently there is no template specialisation of
> 'reverse' that handles narrow strings, you might want to file an enhancement
> request.

That seems correct, the `reverse' function tests for
`isBidirectionalRange' and `hasSwappableElements'

The following code shows the results

import std.range;
import std.stdio;
import std.conv;

void main() {
    char[] char_array = ['a','b','c'];
    ubyte[] ubyte_array = ['a','b','c'];

    writefln("isBidirectonalRange char_array:\t%s",
        to!string(isBidirectionalRange!(typeof(char_array))));
    writefln("isBidirectonalRange ubyte_array:\t%s",
        to!string(isBidirectionalRange!(typeof(ubyte_array))));

    writefln("hasSwappableElements char_array:\t%s",
        to!string(hasSwappableElements!(typeof(char_array))));
    writefln("hasSwappableElements ubyte_array:\t%s",
        to!string(hasSwappableElements!(typeof(ubyte_array))));

}

The output is


isBidirectonalRange char_array:	true
isBidirectonalRange ubyte_array:	true
hasSwappableElements char_array:	false
hasSwappableElements ubyte_array:	true

So if just just need an array of bytes and the `char' semantics are
unimportant, then you can just use a ubyte instead. However Timon is
correct that there should probably be a narrow string version of
`reverse'.

James Miller