Add blockchain example

relax type bounds on struct definition

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "pow"
-version = "0.1.4"
+version = "0.1.5"
 authors = ["Andrew Dirksen <andrew@dirksen.com>"]
 description = """
 Generate or verify sha256 based proofs of work over arbitrary typed data.

readme.md

@@ -30,6 +30,16 @@ let pw = Pow::prove_work(&now, difficulty).unwrap();
 assert!(pw.score(&now).unwrap() >= difficulty);
 ```
 
+Define a blockchain block.
+
+```rust
+struct Block<T> {
+    prev: [u8; 32], // hash of last block
+    payload: T,     // generic data
+    proof_of_work: Pow<([u8; 32], T)>,
+}
+```
+
 # Score scheme
 
 To score a proof of work for a given (target, Pow) pair:

src/lib.rs

@@ -33,7 +33,18 @@
 //! let pw = Pow::prove_work(&now, difficulty).unwrap();
 //! assert!(pw.score(&now).unwrap() >= difficulty);
 //! ```
-
+//!
+//! Define a blockchain block.
+//!
+//! ```rust
+//! # use pow::Pow;
+//! struct Block<T> {
+//!     prev: [u8; 32], // hash of last block
+//!     payload: T,     // generic data
+//!     proof_of_work: Pow<([u8; 32], T)>,
+//! }
+//! ```
+//!
 //! # Score scheme
 //!
 //! To score a proof of work for a given (target, Pow) pair:

src/proof_of_work.rs

@@ -6,7 +6,7 @@ const SALT: &str = "35af8f4890981391c191e6df45b5f780812ddf0213f29299576ac1c98e18
 
 /// Proof of work over concrete type T. T can be any type that implements serde::Serialize.
 #[derive(Serialize, Deserialize, PartialEq, Clone, Copy, Debug)]
-pub struct Pow<T: Serialize> {
+pub struct Pow<T> {
     proof: u128,
     _spook: PhantomData<T>,
 }