@serco #30
说得对，crate json 要比 serde_json 快一倍（ AMD Ryzen 7 5800U ）

```rs
// build with cargo build -r
use std::fs::File;
use std::io::{Read};

use serde_json::Value;
use json;

fn parse_json(contents: &Vec<u8>) {
let now = std::time::Instant::now();
let _: Value = serde_json::from_slice(&contents).unwrap();
let elapsed = now.elapsed();
println!("serde_json: {:?}", elapsed);
}

fn parse_json2(contents: &str) {
let now = std::time::Instant::now();
let _ = json::parse(&contents).unwrap();
let elapsed = now.elapsed();
println!("json: {:?}", elapsed);
}

fn main() {
let contents = {
let mut vec = Vec::new();
// https://github.com/json-iterator/test-data/blob/master/large-file.json
File::open("large-file.json").unwrap().read_to_end(&mut vec).unwrap();
vec
};
for _ in 0..10 {
parse_json(&contents);
}
for _ in 0..10 {
// create json str from contents
let contents = String::from_utf8(contents.clone()).unwrap();
parse_json2(&contents);
}
}

```

```
serde_json: 182.566705ms
serde_json: 157.330185ms
serde_json: 151.551179ms
serde_json: 150.997928ms
serde_json: 158.290287ms
serde_json: 151.983899ms
serde_json: 152.493476ms
serde_json: 150.337436ms
serde_json: 151.174303ms
serde_json: 150.424319ms
json: 71.080736ms
json: 73.125015ms
json: 80.531158ms
json: 82.744729ms
json: 79.73645ms
json: 80.040878ms
json: 80.30521ms
json: 79.455428ms
json: 79.702968ms
json: 72.22127ms

________________________________________________________
Executed in 2.42 secs fish external
usr time 2.36 secs 0.00 micros 2.36 secs
sys time 0.06 secs 464.00 micros 0.06 secs
```

当然，你换个编程语言也可以比 serde_json 更快

```fs
/// build with dotnet build -c Release
open System.IO
open System.Text.Json
open System.Diagnostics

let json = File.ReadAllText("large-file.json")

for i in 1..10 do
let sw = Stopwatch.StartNew()
let jsonDocument = JsonDocument.Parse(json)
sw.Stop()
// print in ms
printfn "Elapsed: %dms" sw.ElapsedMilliseconds

printf "Done"
```

```
Elapsed: 185ms
Elapsed: 74ms
Elapsed: 73ms
Elapsed: 70ms
Elapsed: 75ms
Elapsed: 74ms
Elapsed: 67ms
Elapsed: 69ms
Elapsed: 73ms
Elapsed: 73ms
Done
________________________________________________________
Executed in 963.57 millis fish external
usr time 881.76 millis 0.00 micros 881.76 millis
sys time 86.87 millis 387.00 micros 86.48 millis
```