Add some box-related methods (#79)

* Adds box-related methods

CHANGELOG.md

@@ -5,10 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+
 ## [Unreleased]
 
 ### Added
 
+-   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.
 

src/pointer.rs

@@ -1,6 +1,7 @@
 use crate::{token::InvalidEncodingError, Components, Token, Tokens};
 use alloc::{
     borrow::ToOwned,
+    boxed::Box,
     fmt,
     string::{String, ToString},
     vec::Vec,
@@ -558,6 +559,14 @@ impl Pointer {
     pub fn is_empty(&self) -> bool {
         self.0.is_empty()
     }
+
+    /// Converts a `Box<Pointer>` into a `PointerBuf` without copying or allocating.
+    pub fn into_buf(self: Box<Pointer>) -> PointerBuf {
+        let inner = Box::into_raw(self);
+        // SAFETY: we ensure the layout of `Pointer` is the same as `str`
+        let inner = unsafe { Box::<str>::from_raw(inner as *mut str) };
+        PointerBuf(inner.into_string())
+    }
 }
 
 #[cfg(feature = "serde")]
@@ -1002,6 +1011,14 @@ impl Deref for PointerBuf {
     }
 }
 
+impl From<PointerBuf> for Box<Pointer> {
+    fn from(value: PointerBuf) -> Self {
+        let s = value.0.into_boxed_str();
+        // SAFETY: we ensure that the layout of `str` is the same as `Pointer`
+        unsafe { Box::from_raw(Box::into_raw(s) as *mut Pointer) }
+    }
+}
+
 #[cfg(feature = "serde")]
 impl<'de> serde::Deserialize<'de> for PointerBuf {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
@@ -2212,4 +2229,12 @@ mod tests {
         let borrowed: &Pointer = ptr.borrow();
         assert_eq!(borrowed, "/foo/bar");
     }
+
+    #[test]
+    fn from_box_to_buf() {
+        let original = PointerBuf::parse("/foo/bar/0").unwrap();
+        let boxed: Box<Pointer> = original.clone().into();
+        let unboxed = boxed.into_buf();
+        assert_eq!(original, unboxed);
+    }
 }