Have you any tips for using D when you need fast string concatenation? I regularly use code like this:

    foreach (i, range)
    {
        foo ~= bar;
    }

or:

    foo = foo ~ bar ~ baz ~ qux;

I've used std.string.format(...) in some instances which sped things up which surprised me.

Are there faster ways of appending strings?

On Friday, 21 June 2013 at 10:09:10 UTC, Gary Willoughby wrote:
> Are there faster ways of appending strings?

You'll want to use appender, from std.array:

http://dlang.org/phobos/std_array.html#.Appender

On Friday, June 21, 2013 12:09:09 Gary Willoughby wrote:
> Have you any tips for using D when you need fast string concatenation? I regularly use code like this:
> 
>      foreach (i, range)
>      {
>          foo ~= bar;
>      }
> 
> or:
> 
>      foo = foo ~ bar ~ baz ~ qux;
> 
> I've used std.string.format(...) in some instances which sped
> things up which surprised me.
> 
> Are there faster ways of appending strings?

In general, ~= will be faster, beacause it won't create temporaries like concatenating a bunch of strings in a single expression would. However, if you want faster appending, generally the thing to use is std.array.Appender. And if you want to use format strings, it can be used with std.format.formattedWrite.

- Jonathan M Davis

On Friday, 21 June 2013 at 10:09:10 UTC, Gary Willoughby wrote:
> Have you any tips for using D when you need fast string concatenation? I regularly use code like this:
>
>     foreach (i, range)
>     {
>         foo ~= bar;
>     }
>
> or:
>
>     foo = foo ~ bar ~ baz ~ qux;
>
> I've used std.string.format(...) in some instances which sped things up which surprised me.
>
> Are there faster ways of appending strings?

Regardless of whether you end up using lots of ~=, or Appender (possibly with formattedWrite), using reserve never hurts.

On Friday, 21 June 2013 at 11:33:29 UTC, monarch_dodra wrote:
> On Friday, 21 June 2013 at 10:09:10 UTC, Gary Willoughby wrote:
>> Have you any tips for using D when you need fast string concatenation? I regularly use code like this:
>>
>>    foreach (i, range)
>>    {
>>        foo ~= bar;
>>    }
>>
>> or:
>>
>>    foo = foo ~ bar ~ baz ~ qux;
>>
>> I've used std.string.format(...) in some instances which sped things up which surprised me.
>>
>> Are there faster ways of appending strings?
>
> Regardless of whether you end up using lots of ~=, or Appender (possibly with formattedWrite), using reserve never hurts.


It's worth pointing out that Appender supports ~= so it's very easy to swap it in, replacing builtin concatenation.

> It's worth pointing out that Appender supports ~= so it's very easy to swap it in, replacing builtin concatenation.

This works since 2.062 AFAIK. So is still quite new.

On Fri, 21 Jun 2013 06:14:38 -0400, Jonathan M Davis <jmdavisProg@gmx.com> wrote:

> On Friday, June 21, 2013 12:09:09 Gary Willoughby wrote:
>> Have you any tips for using D when you need fast string
>> concatenation? I regularly use code like this:
>>
>>      foreach (i, range)
>>      {
>>          foo ~= bar;
>>      }
>>
>> or:
>>
>>      foo = foo ~ bar ~ baz ~ qux;
>>
>> I've used std.string.format(...) in some instances which sped
>> things up which surprised me.
>>
>> Are there faster ways of appending strings?
>
> In general, ~= will be faster, beacause it won't create temporaries like
> concatenating a bunch of strings in a single expression would.

I believe the above is one call to the runtime.

To answer the OP, using reserve will speed up the allocation quite a bit.  Appender is certainly the fastest method.

-Steve