rust/tests/ui/slow_vector_initialization.rs

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use std::iter::repeat;
fn main() {
resize_vector();
extend_vector();
mixed_extend_resize_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));
let mut vec4 = Vec::with_capacity(len);
vec4.extend(repeat(0).take(vec4.capacity()));
}
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);
let mut vec4 = Vec::with_capacity(len);
vec4.resize(vec4.capacity(), 0);
// Reinitialization should be warned
vec1 = Vec::with_capacity(10);
vec1.resize(10, 0);
}
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fn do_stuff(vec: &mut [u8]) {}
fn extend_vector_with_manipulations_between() {
let len = 300;
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let mut vec1: Vec<u8> = Vec::with_capacity(len);
do_stuff(&mut vec1);
vec1.extend(repeat(0).take(len));
}