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@Swatinem
Created December 2, 2015 20:35
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#![feature(alloc)]
#![feature(heap_api)]
extern crate alloc;
use alloc::heap::{usable_size};
use std::mem::{align_of, size_of};
use std::str::{from_utf8};
fn print_vec_sizes<T>(v: &Vec<T>) {
let elem_size = size_of::<T>();
let elem_align = align_of::<T>();
let cap = v.capacity();
let actual = elem_size * cap;
let usable = usable_size(actual, elem_align);
let possible = usable / elem_size;
println!("item size/align: {:#?}/{:#?} ; cap/mem: {:#?}/{:#?} ; usable cap/mem {:#?}/{:#?}",
elem_size, elem_align, cap, actual, possible, usable);
}
fn print_string_sizes(s: &mut String) {
unsafe {
print_vec_sizes(s.as_mut_vec());
}
}
fn main() {
let mut v: Vec<u32> = Vec::new();
v.push(1);
print_vec_sizes(&v);
v.reserve(1024);
print_vec_sizes(&v);
v.extend([1; 1025].iter());
print_vec_sizes(&v);
let mut s = String::new();
s.extend("a".chars());
print_string_sizes(&mut s);
s.reserve(1024);
print_string_sizes(&mut s);
s.extend(from_utf8(&[97u8; 1025]).unwrap().chars());
print_string_sizes(&mut s);
}
item size/align: 4/4 ; cap/mem: 4/16 ; usable cap/mem 4/16
item size/align: 4/4 ; cap/mem: 1025/4100 ; usable cap/mem 2048/8192
item size/align: 4/4 ; cap/mem: 2050/8200 ; usable cap/mem 3072/12288
item size/align: 1/1 ; cap/mem: 1/1 ; usable cap/mem 8/8
item size/align: 1/1 ; cap/mem: 1025/1025 ; usable cap/mem 1280/1280
item size/align: 1/1 ; cap/mem: 2050/2050 ; usable cap/mem 2560/2560
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