151 lines
4.3 KiB
Rust
151 lines
4.3 KiB
Rust
use std::iter::Iterator;
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/// A helper for building a string in-order based on an original string and a
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/// series of insertions, deletions, and copies applied to it. It is safe to use
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/// with UTF-8 strings as all operations are based on character indices. The
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/// methods must be called in-order.
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pub struct StringBuilder<'a> {
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original: Box<dyn Iterator<Item = char> + 'a>,
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buffer: String,
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#[cfg(debug_assertions)]
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remaining: String,
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}
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impl StringBuilder<'_> {
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pub fn new(original: &str) -> StringBuilder<'_> {
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StringBuilder {
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original: Box::new(original.chars()),
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buffer: String::with_capacity(original.len()),
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#[cfg(debug_assertions)]
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remaining: original.to_owned(),
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}
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}
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/// Insert a string at the end of the built buffer.
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pub fn insert(&mut self, text: &str) { self.buffer.push_str(text); }
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/// Skip copying `length` characters from the original string to the built
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/// buffer.
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pub fn delete(&mut self, length: usize) {
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if length == 0 {
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return;
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}
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self.original.nth(length - 1);
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if cfg!(debug_assertions) {
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self.remaining = self.remaining.chars().skip(length).collect();
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}
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}
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/// Copy `length` characters from the original string to the built buffer.
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pub fn retain(&mut self, length: usize) {
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self.buffer.extend(self.original.by_ref().take(length));
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if cfg!(debug_assertions) {
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self.remaining = self.remaining.chars().skip(length).collect();
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}
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}
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/// Finish building the string after copying the remaining original string
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/// since the last insertion or deletion.
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pub fn build(self) -> String { self.buffer }
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#[cfg(debug_assertions)]
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/// Get a slice of the remaining original string. The slice starts from
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/// where the next delete/retain operation would start and is of length
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/// `length`. The implementation is quite suboptimal but it's only used
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/// for debugging.
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pub fn get_slice_from_remaining(&self, length: usize) -> String {
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let result = self.remaining.chars().take(length).collect::<String>();
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debug_assert_eq!(result.chars().count(), length, "Range out of bounds");
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result
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}
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}
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#[cfg(test)]
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mod tests {
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use pretty_assertions::assert_eq;
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use super::*;
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#[test]
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fn test_string_builder() {
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let original = "aaa bbb ccc";
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let mut builder = StringBuilder::new(original);
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builder.insert("ddd");
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builder.delete(3);
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builder.retain(8);
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builder.insert(" eee");
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assert_eq!(builder.build(), "ddd bbb ccc eee");
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let original = "abcde";
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let mut builder = StringBuilder::new(original);
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builder.retain(1);
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builder.delete(3);
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builder.retain(1);
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assert_eq!(builder.build(), "ae");
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}
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#[test]
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fn test_empty_original() {
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let original = "";
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let mut builder = StringBuilder::new(original);
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builder.insert("test");
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assert_eq!(builder.build(), "test");
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}
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#[test]
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fn test_unicode_characters() {
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let original = "こんにちは";
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let mut builder = StringBuilder::new(original);
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builder.retain(3);
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builder.insert("世界, "); // Insert "World, "
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builder.retain(2);
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assert_eq!(builder.build(), "こんに世界, ちは");
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}
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#[test]
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fn test_get_slice() {
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let original = "abcdef";
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let builder = StringBuilder::new(original);
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// Test getting a slice of the original string
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assert_eq!(builder.get_slice_from_remaining(3), "abc");
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// Test getting a slice that includes both buffer and remaining original
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let mut builder = StringBuilder::new(original);
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builder.retain(2); // "ab" in buffer
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assert_eq!(builder.get_slice_from_remaining(2), "cd");
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}
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#[test]
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fn test_retain_all() {
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let original = "Hello, world!";
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let mut builder = StringBuilder::new(original);
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builder.retain(original.len());
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assert_eq!(builder.build(), original);
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}
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#[test]
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fn test_delete_all() {
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let original = "Hello";
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let mut builder = StringBuilder::new(original);
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builder.delete(original.len());
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builder.insert("Hi");
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assert_eq!(builder.build(), "Hi");
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}
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}
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