Slicing API for Pointer (#84)

* implement slicing api

* update changelog

* add note about complexity of indexing tokens

Author: asmello

CHANGELOG.md

@@ -20,6 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 -   Changed signature of `PathBuf::parse` to avoid requiring allocation.
 -   Bumps minimum Rust version to 1.79.
+-   `Pointer::get` now accepts ranges and can produce `Pointer` segments as output (similar to
+    `slice::get`).
 
 ### Fixed
 

src/pointer.rs

@@ -7,6 +7,9 @@ use alloc::{
     vec::Vec,
 };
 use core::{borrow::Borrow, cmp::Ordering, ops::Deref, str::FromStr};
+use slice::SlicePointer;
+
+mod slice;
 
 /*
 ░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
@@ -277,23 +280,35 @@ impl Pointer {
             .map(|s| unsafe { Self::new_unchecked(s) })
     }
 
-    /// Attempts to get a `Token` by the index. Returns `None` if the index is
-    /// out of bounds.
+    /// Attempts to get a `Token` or a segment of the `Pointer`, depending on
+    /// the type of index.
+    ///
+    /// Returns `None` if the index is out of bounds.
+    ///
+    /// Note that this operation is O(n).
     ///
     /// ## Example
     /// ```rust
     /// use jsonptr::{Pointer, Token};
     ///
-    /// let ptr = Pointer::from_static("/foo/bar");
+    /// let ptr = Pointer::from_static("/foo/bar/qux");
     /// assert_eq!(ptr.get(0), Some("foo".into()));
     /// assert_eq!(ptr.get(1), Some("bar".into()));
-    /// assert_eq!(ptr.get(2), None);
+    /// assert_eq!(ptr.get(3), None);
+    /// assert_eq!(ptr.get(..), Some(Pointer::from_static("/foo/bar/qux")));
+    /// assert_eq!(ptr.get(..1), Some(Pointer::from_static("/foo")));
+    /// assert_eq!(ptr.get(1..3), Some(Pointer::from_static("/bar/qux")));
+    /// assert_eq!(ptr.get(1..=2), Some(Pointer::from_static("/bar/qux")));
     ///
     /// let ptr = Pointer::root();
     /// assert_eq!(ptr.get(0), None);
+    /// assert_eq!(ptr.get(..), Some(Pointer::root()));
     /// ```
-    pub fn get(&self, index: usize) -> Option<Token> {
-        self.tokens().nth(index).clone()
+    pub fn get<'p, I>(&'p self, index: I) -> Option<I::Output>
+    where
+        I: SlicePointer<'p>,
+    {
+        index.get(self)
     }
 
     /// Attempts to resolve a [`R::Value`] based on the path in this [`Pointer`].