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Optimize deserialization of recursive buffered types #2148

merged 1 commit into from Jan 1, 2022


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@dtolnay dtolnay commented Jan 1, 2022

Closes #2146.

@dtolnay dtolnay merged commit 1f57084 into master Jan 1, 2022
@dtolnay dtolnay deleted the deserializecontent branch January 1, 2022 21:16
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dtolnay commented Jan 2, 2022



extern crate test;

use serde::{Deserialize, Serialize};
use std::collections::BTreeMap as Map;

#[derive(Deserialize, Serialize)]
#[serde(tag = "type")]
enum Enum {
    Rec(Map<String, Enum>),

fn bench(b: &mut test::Bencher) {
    let j = serde_json::to_string(&obj()).unwrap();
    b.iter(|| serde_json::from_str::<Enum>(&j).unwrap());

fn obj() -> Enum {
    let mut map = Map::new();
    for i in 0..100 {
        let mut outer = Map::new();
        outer.insert(i.to_string(), Enum::Rec(map));
        map = outer;
  • Before: 834 μs/iter
  • After: 49 μs/iter

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Improve performance using nightly features
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