add pointer tag

Cargo.toml

@@ -13,8 +13,6 @@ categories = ["data-structures", "memory-management", "no-std"]
 include = ["Cargo.toml", "LICENSE", "src", "README.md"]
 rust-version = "1.34.2"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
 sptr = "0.3.1"
 

src/lib.rs

@@ -92,6 +92,7 @@ extern crate alloc; // we want that for tests so we can use `Box`
 
 mod backend;
 mod strategy;
+mod tag;
 
 use core::{
     fmt::{Debug, Formatter},

src/tag.rs

@@ -0,0 +1,17 @@
+use core::marker::PhantomData;
+
+use crate::Backend;
+
+pub struct TaggedPtr<T, S, B = usize>(B::Stored, PhantomData<S>)
+where
+    B: Backend<T>;
+
+pub trait TaggingStrategy<B> {
+    type Tag;
+
+    fn get_tag(data: B) -> Self::Tag;
+
+    fn get_ptr_addr(data: B) -> usize;
+
+    fn set(addr: usize, tag: Self::Tag) -> B;
+}