rust-clippy/tests/ui/slow_vector_initialization.rs

// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::iter::repeat;

fn main() {
    resize_vector();
    extend_vector();
    mixed_extend_resize_vector();
    unsafe_vector();
}

fn extend_vector() {
    // Extend with constant expression
    let len = 300;
    let mut vec1 = Vec::with_capacity(len);
    vec1.extend(repeat(0).take(len));

    // Extend with len expression
    let mut vec2 = Vec::with_capacity(len - 10);
    vec2.extend(repeat(0).take(len - 10));

    // Extend with mismatching expression should not be warned
    let mut vec3 = Vec::with_capacity(24322);
    vec3.extend(repeat(0).take(2));
}

fn mixed_extend_resize_vector() {
    // Mismatching len
    let mut mismatching_len = Vec::with_capacity(30);
    mismatching_len.extend(repeat(0).take(40));

    // Slow initialization
    let mut resized_vec = Vec::with_capacity(30);
    resized_vec.resize(30, 0);

    let mut extend_vec = Vec::with_capacity(30);
    extend_vec.extend(repeat(0).take(30));
}

fn resize_vector() {
    // Resize with constant expression
    let len = 300;
    let mut vec1 = Vec::with_capacity(len);
    vec1.resize(len, 0);

    // Resize mismatch len
    let mut vec2 = Vec::with_capacity(200);
    vec2.resize(10, 0);

    // Resize with len expression
    let mut vec3 = Vec::with_capacity(len - 10);
    vec3.resize(len - 10, 0);

    // Reinitialization should be warned
    vec1 = Vec::with_capacity(10);
    vec1.resize(10, 0);
}

fn unsafe_vector() {
    let mut unsafe_vec: Vec<u8> = Vec::with_capacity(200);

    unsafe {
        unsafe_vec.set_len(200);
    }
}

fn do_stuff(vec: &mut Vec<u8>) {

}

fn extend_vector_with_manipulations_between() {
    let len = 300;
    let mut vec1:Vec<u8> = Vec::with_capacity(len);
    do_stuff(&mut vec1);
    vec1.extend(repeat(0).take(len));
}