jonhoo · April 22, 2020 22:08 · Apr 22, 2020
diff --git a/strsplit.rs b/strsplit.rs
@@ -0,0 +1,76 @@
+#![warn(rust_2018_idioms)]
+
+#[derive(Debug)]
+pub struct StrSplit<'haystack, D> {
+    remainder: Option<&'haystack str>,
+    delimiter: D,
+}
+
+impl<'haystack, D> StrSplit<'haystack, D> {
+    pub fn new(haystack: &'haystack str, delimiter: D) -> Self {
+        Self {
+            remainder: Some(haystack),
+            delimiter,
+        }
+    }
+}
+
+pub trait Delimiter {
+    fn find_next(&self, s: &str) -> Option<(usize, usize)>;
+}
+
+impl<'haystack, D> Iterator for StrSplit<'haystack, D>
+where
+    D: Delimiter,
+{
+    type Item = &'haystack str;
+    fn next(&mut self) -> Option<Self::Item> {
+        let remainder = self.remainder.as_mut()?;
+        if let Some((delim_start, delim_end)) = self.delimiter.find_next(remainder) {
+            let until_delimiter = &remainder[..delim_start];
+            *remainder = &remainder[delim_end..];
+            Some(until_delimiter)
+        } else {
+            self.remainder.take()
+        }
+    }
+}
+
+impl Delimiter for &str {
+    fn find_next(&self, s: &str) -> Option<(usize, usize)> {
+        s.find(self).map(|start| (start, start + self.len()))
+    }
+}
+
+impl Delimiter for char {
+    fn find_next(&self, s: &str) -> Option<(usize, usize)> {
+        s.char_indices()
+            .find(|(_, c)| c == self)
+            .map(|(start, _)| (start, start + self.len_utf8()))
+    }
+}
+
+pub fn until_char(s: &str, c: char) -> &'_ str {
+    StrSplit::new(s, c)
+        .next()
+        .expect("StrSplit always gives at least one result")
+}
+
+#[test]
+fn until_char_test() {
+    assert_eq!(until_char("hello world", 'o'), "hell");
+}
+
+#[test]
+fn it_works() {
+    let haystack = "a b c d e";
+    let letters: Vec<_> = StrSplit::new(haystack, " ").collect();
+    assert_eq!(letters, vec!["a", "b", "c", "d", "e"]);
+}
+
+#[test]
+fn tail() {
+    let haystack = "a b c d ";
+    let letters: Vec<_> = StrSplit::new(haystack, " ").collect();
+    assert_eq!(letters, vec!["a", "b", "c", "d", ""]);
+}