Re: Appender is ... slow

[Philippe Sigaud via Digitalmars-d-learn]

> I wonder if using plain `Array` instead may be result in better performance
> where immutability is not needed.

Hmm, no:

module appendertest;

import std.array;
import std.datetime;
import std.stdio;
import std.container;

enum size = 1_000;

void test1()
{
    auto arr = appender!(int[])();
    foreach(n; 0 .. size)
        arr.put(n);
}

void test1prime()
{
    auto arr = appender!(int[])();
    foreach(n; 0 .. size)
        arr ~= n;
}

void test2()
{
    int[] arr;
    foreach(n; 0 .. size)
        arr ~= n;
}

void test2prime()
{
    int[] arr;
    arr.reserve(size);
    foreach(n; 0 .. size)
        arr ~= n;
}

void test3()
{
    Array!int arr;
    foreach(n; 0 .. size)
        arr ~= n;
}

void test3prime()
{
    Array!int arr;
    arr.reserve(size);
    foreach(n; 0 .. size)
        arr ~= n;
}

void test4()
{
    auto arr = new int[](size);
    foreach(n; 0 .. size)
        arr[n] = n;
}

void test5()
{
    auto arr = uninitializedArray!(int[])(size);
    foreach(n; 0 .. size)
        arr[n] = n;
}

void main()
{
    auto result = benchmark!(test1, test1prime,
                             test2, test2prime,
                             test3, test3prime,
                             test4,
                             test5
                            )(10_000);

    writeln("Appender.put       :", cast(Duration)result[0]);
    writeln("Appender ~=        :", cast(Duration)result[1]);
    writeln("Std array          :", cast(Duration)result[2]);
    writeln("Std array.reserve  :", cast(Duration)result[3]);
    writeln("Array              :", cast(Duration)result[4]);
    writeln("Array.reserve      :", cast(Duration)result[5]);
    writeln("new T[]()          :", cast(Duration)result[6]);
    writeln("uninitializedArray :", cast(Duration)result[7]);
}

Times:

Appender.put       :157 ms, 602 μs, and 3 hnsecs
Appender ~=        :182 ms, 807 μs, and 1 hnsec
Std array          :256 ms, 210 μs, and 7 hnsecs
Std array.reserve  :244 ms, 770 μs, and 4 hnsecs
Array              :336 ms, 207 μs, and 3 hnsecs
Array.reserve      :321 ms, 500 μs, and 6 hnsecs
new T[]()          :28 ms, 496 μs, and 6 hnsecs
uninitializedArray :26 ms and 620 μs