ср, 13 июл. 2016 г. в 16:41, Branimir Maksimovic <branimir.maksimovic@gmail.com>:

rust (no need for array but anyway)

[bmaxa@manjaro rust]$ time ./append
10000000 took 0.064016791
110000000 took 0.13466229

real    0m0.204s
user    0m0.167s
sys    0m0.033s

haskell (your fastest version)

[bmaxa@manjaro rust]$ time ./concat
"Done"

real    0m0.224s
user    0m0.220s
sys    0m0.000s

c++ (no array)

[bmaxa@manjaro rust]$ time ./a.out

real    0m0.115s
user    0m0.100s
sys    0m0.013s

rust:

use std::time::*;

fn main() {
    let mut arr=Vec::new();
    arr.reserve(10_000_000);
    let start = Instant::now();
    for _ in 0 .. 10_000_000 {
        arr.push("hello world");
    }
    let end = start.elapsed();
    let diff = (end.as_secs()*1000000000 + end.subsec_nanos() as u64) as f64/1000000000.;
    println!("{} took {}",arr.len(),diff);
    let mut str = String::new();
    str.reserve(110_000_000);
    let start = Instant::now();
    for i in arr {
        str .push_str(i);
    }
    let end = start.elapsed();
    let diff = (end.as_secs()*1000000000 + end.subsec_nanos() as u64) as f64/1000000000.;
    println!("{} took {}",str.len(),diff);
}

c++:

#include <stdio.h>
#include <string>

int main() {
    std::string tmp;
    tmp.reserve(110000000);
    for (int i=0;i<10000000;i++) {
        tmp += "hello world";
    }
}

Model name:            Intel(R) Core(TM) i3-5005U CPU @ 2.00GHz
On 07/12/2016 05:36 AM, William Yager wrote:
You picked the single slowest way to do it. Please see https://gist.github.com/wyager/df063ad4edd9a9c8b0ab762c91a79894

All times are on my Intel Atom Macbook. Compiled with -O3, no other options.

Using Lazy Bytestrings (either through the Builder interface or plain old concatenation) is about 7-7.5 times faster than string concatenation so on your computer it should take about 0.12 seconds. In other words, faster than C.

This is my usual experience with lazy bytestrings; due to their optimization for cache size, they are extremely fast with almost no effort. They often out-perform "fast" array operations in C due to fusion and cache coherency.

I will note that if you want to do exactly what C does (often with only slightly different assembly output), you can often achieve this with unboxed vectors (mutable or immutable, depending on your application).

--Will

On Mon, Jul 11, 2016 at 10:24 PM, Richard A. O'Keefe <ok@cs.otago.ac.nz> wrote:

Making a list of "Hello world" 10,000,000 times and then
concatenating that list to produce a single String took
0.87 seconds (start program to end program) in Haskell.
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