serde_derive 1.0.25 on Rust Cargo

Add the following function with default implementation to the Deserialize trait (thanks @gankro!)

fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
where
    D: Deserializer<'de>,
{
    *place = Deserialize::deserialize(deserializer)?;
    Ok(())
}

This is a power user feature that allows deserialization to reuse existing allocations for types like String and Vec. Enable the deserialize_in_place feature of serde_derive to generate these efficient implementations for all types that use #[derive(Deserialize)].

extern crate serde;
extern crate serde_json;

use serde::Deserialize;

fn main() {
    let mut v = Vec::<i32>::with_capacity(128);
    assert_eq!(v.capacity(), 128);

    let j = "[1, 2, 3]";
    let ref mut de = serde_json::Deserializer::from_str(j);
    Deserialize::deserialize_in_place(de, &mut v).unwrap();
    assert_eq!(v, [1, 2, 3]);
    assert_eq!(v.capacity(), 128);
}