Add Pointer::starts_with and Pointer::ends_with (#81)

* add starts_with and ends_with

* update changelog

CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Adds method `into_buf` for `Box<Pointer>` and `impl From<PathBuf> for Box<Pointer>`. 
 - Adds unsafe associated methods `Pointer::new_unchecked` and `PointerBuf::new_unchecked` for
  external zero-cost construction.
+- Adds `Pointer::starts_with` and `Pointer::ends_with` for prefix and suffix matching.
 - Adds new `ParseIndexError` variant to express the presence non-digit characters in the token.
 - Adds `Token::is_next` for checking if a token represents the `-` character.
 

src/pointer.rs

@@ -280,12 +280,26 @@ impl Pointer {
  .map(|s| unsafe { Self::new_unchecked(s) })
  }
 
- /// Attempts to get a `Token` or a segment of the `Pointer`, depending on
- /// the type of index.
+ /// Returns whether `self` has a suffix of `other`.
  ///
- /// Returns `None` if the index is out of bounds.
+ /// Note that `Pointer::root` is only a valid suffix of itself.
+ pub fn ends_with(&self, other: &Self) -> bool {
+ (self.is_root() && other.is_root())
+ || (!other.is_root() && self.as_str().ends_with(&other.0))
+ }
+
+ /// Returns whether `self` has a prefix of `other.`
  ///
- /// Note that this operation is O(n).
+ /// Note that `Pointer::root` is a valid prefix of any `Pointer` (including
+ /// itself).
+ pub fn starts_with(&self, other: &Self) -> bool {
+ self.as_str().starts_with(&other.0)
+ // ensure we end at a token boundary
+ && (other.len() == self.len() || self.0.as_bytes()[other.len()] == b'/')
+ }
+
+ /// Attempts to get a `Token` by the index. Returns `None` if the index is
+ /// out of bounds.
  ///
  /// ## Example
  /// ```rust
@@ -1372,6 +1386,58 @@ mod tests {
  assert_eq!(stripped, "/to/some/value");
  }
 
+ #[test]
+ fn ends_with() {
+ // positive cases
+ let p = Pointer::from_static("/foo/bar");
+ let q = Pointer::from_static("/bar");
+ assert!(p.ends_with(q));
+ let q = Pointer::from_static("/foo/bar");
+ assert!(p.ends_with(q));
+
+ // negative cases
+ let q = Pointer::from_static("/barz");
+ assert!(!p.ends_with(q));
+ let q = Pointer::from_static("/");
+ assert!(!p.ends_with(q));
+ let q = Pointer::from_static("");
+ assert!(!p.ends_with(q));
+ let q = Pointer::from_static("/qux/foo/bar");
+ assert!(!p.ends_with(q));
+
+ // edge case - both root
+ let p = Pointer::root();
+ let q = Pointer::root();
+ assert!(p.ends_with(q));
+ }
+
+ #[test]
+ fn starts_with() {
+ // positive cases
+ let p = Pointer::from_static("/foo/bar");
+ let q = Pointer::from_static("/foo");
+ assert!(p.starts_with(q));
+ let q = Pointer::from_static("/foo/bar");
+ assert!(p.starts_with(q));
+
+ // negative cases
+ let q = Pointer::from_static("/");
+ assert!(!p.starts_with(q));
+ let q = Pointer::from_static("/fo");
+ assert!(!p.starts_with(q));
+ let q = Pointer::from_static("/foo/");
+ assert!(!p.starts_with(q));
+
+ // edge cases: other is root
+ let p = Pointer::root();
+ let q = Pointer::root();
+ assert!(p.starts_with(q));
+ let p = Pointer::from_static("/");
+ assert!(p.starts_with(q));
+ let p = Pointer::from_static("/any/thing");
+ assert!(p.starts_with(q));
+ }
+
  #[test]
  fn parse_error_is_no_leading_backslash() {
  let err = ParseError::NoLeadingBackslash;