Substring

prelude.rs

use std::ops::{Bound, RangeBounds};

/// Utilities to take a substring of a string slice, taking into account UTF-8.
pub trait StringUtils {
    /// Get a substring of a string slice, with start and length.
    fn substring(&self, start: usize, len: usize) -> &str;
    /// Get a substring of a string slice, with a range.
    fn slice(&self, range: impl RangeBounds<usize>) -> &str;
}

impl StringUtils for str {
    fn substring(&self, start: usize, len: usize) -> &str {
        self.char_indices()
            .nth(start)
            .map(|(start_byte, _)| {
                self.char_indices()
                    .nth(start + len)
                    .map(|(end_byte, _)| &self[start_byte..end_byte])
                    .unwrap_or(&self[start_byte..])
            })
            .unwrap_or("")
    }
    fn slice(&self, range: impl RangeBounds<usize>) -> &str {
        let start = match range.start_bound() {
            Bound::Included(bound) | Bound::Excluded(bound) => *bound,
            Bound::Unbounded => 0,
        };
        let len = match range.end_bound() {
            Bound::Included(bound) => *bound + 1,
            Bound::Excluded(bound) => *bound,
            Bound::Unbounded => self.len(),
        } - start;
        self.substring(start, len)
    }
}