Add methods to String which can remove multiple elements at once

text/0000-remove-range.md

@@ -0,0 +1,55 @@
+- Start Date: 2015-01-11
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+
+Add a method to `String` that allow the user to remove more than
+one character at a time while preserving the order of the remaining
+characters.
+
+# Motivation
+
+`String`currently contains the following safe methods related to this proposal:
+
+- `String::pop`, and
+- `String::remove`.
+
+`String::pop` remove a single character from the end of the string.
+
+`String::remove` allows the user to remove a single character anywhere in the string by shifting the rest of the string one slot to the left.
+
+For example, given the `String` "さび", which is internally represented as the
+`Vec<u8>` `[0xe3, 0x81, 0x95, 0xe3, 0x81, 0xb3]`, `String::remove(0)` removes
+the first 3 bytes.
+
+This RFC proposes adding the following method:
+
+- `String::remove_range<T: SomeTrait>(&mut self, range: T)`.
+
+Leaving performance aside, calling `String::remove_range(n..m)` is equivalent
+to calling `String::remove(n)` once for every character in the `[n, m)` range.
+
+This method are necessary to remove multiple characters in a performant manner.
+Calling `String::remove` `n` times has `O(n * String::len)` performance instead of
+`O(String::len)` which can be achieved with `String::remove_range`.
+
+One application of these methods is displaying text in user interfaces. More
+precisely: Using `Backspace` inside a text box will remove a grapheme which can
+consist of any number of characters. Using `Ctrl-Backspace` will remove a word, etc.
+
+# Detailed design
+
+Add the following method to `String`:
+
+```rust
+/// Removes the characters in the specified range.
+///
+/// # Panics
+///
+/// Panics if the range is decreasing, the upper bound is larger than the length of the
+/// string, or the bounds are not character boundaries.
+fn remove_range<T: SomeTrait>(&mut self, range: T) { }
+```
+
+Where `SomeTrait` should be implemented for all range types.