equivalent of python join?

[Ali Çehreli]

On 12/02/2013 11:32 PM, Jacob Carlborg wrote:

 > On 2013-12-03 07:36, CJS wrote:
 >> In python a common performance tip for joining many strings together is
 >> to use the join method. So, for example, instead of
 >> "a" + "b" + "c"
 >> use
 >> ''.join(["a","b","c"]).
 >> The idea is to avoid creating temporary objects that are immediately
 >> thrown away. It's obviously overkill for such a small number of strings,
 >> though.
 >>
 >> Is there any equivalent method/advice when concatenating many strings
 >> together in D?
 >
 > There's std.algorithm.joiner[1] and std.array.join[2]. I don't know if
 > they're any more efficient than using "~".

They are more efficient in the sense that they are lazy.

 > There's also
 > std.array.Appender[3] if you want to do a lot of appending and want the
 > most efficient way.
 >
 > [1] http://dlang.org/phobos/std_algorithm.html#joiner
 > [2] http://dlang.org/phobos/std_array.html#.join
 > [3] http://dlang.org/phobos/std_array.html#.Appender

There is also the more general std.range.chain. It can join any type of 
range as long as the element types are the same:

import std.stdio;
import std.range;
import std.algorithm;

void main()
{
     auto a_lazy_range_of_ints
         = chain(5.iota,
                 [ 10, 9, 20, 8 ].filter!(a => a < 10));

     // writeln consumes the range eagerly
     writeln(a_lazy_range_of_ints);

     // Prints [0, 1, 2, 3, 4, 9, 8]
}

Ali