Is there any method to create a (const) string with repeat pattern?
I know that, "str".repeat(n) could generate a String, but this generate a String object in every call, which is not very efficient.
If we have something like:
" " == " " * 10;
// or
" " == repeat!(" ", 10);
we could write some beautiful code:
const PADDING: &str = "##########";
// If we have, const PADDING: &str = "#" * 10;, the program will be nicer.
// further, if the repeat is longer(e.g., "#" * 1000), it is very ugly to write it.
// This is why I want a repeat function generates string literals.
const CONTENT: &str = "abcdefghijklmnopqrst"; // to simulate some generated contents.
use std::time::Instant;
fn main() {
let mut left_padding = [1, 4, 2, 8, 5, 7].into_iter().cycle();
let mut right_padding = [1, 4, 2, 8, 5, 7].into_iter().cycle();
let mut content_length = [8, 5, 7, 1, 4, 2].into_iter().map(|x| x * 2).cycle();
let now = Instant::now();
let mut vec=Vec::new();
for _line in 0..10000 {
vec.push(format!(
"{} {} {}",
PADDING.split_at(left_padding.next().unwrap()).0,
CONTENT.split_at(content_length.next().unwrap()).0,
PADDING.split_at(right_padding.next().unwrap()).0,
));
}
println!("{}", now.elapsed().as_nanos());
println!("{}",vec.len())
}
it takes 1822150 ns to finish the format progress, if we use "#".repeat(n) (as shown below), 2609921 ns will be taken to finish the program.
const CONTENT: &str = "abcdefghijklmnopqrst";
use std::time::Instant;
fn main() {
let mut left_padding = [1, 4, 2, 8, 5, 7].into_iter().cycle();
let mut right_padding = [1, 4, 2, 8, 5, 7].into_iter().cycle();
let mut content_length = [8, 5, 7, 1, 4, 2].into_iter().map(|x| x * 2).cycle();
let now = Instant::now();
let mut vec=Vec::new();
for _line in 0..10000 {
vec.push(format!(
"{} {} {}",
"#".repeat(left_padding.next().unwrap()),
CONTENT.split_at(content_length.next().unwrap()).0,
"#".repeat(right_padding.next().unwrap()),
));
}
println!("{}", now.elapsed().as_nanos());
println!("{}",vec.len())
}