std: move the hash docstring over to std::hash.

src/libstd/hash.rs

@@ -8,7 +8,58 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-//! Generic hashing support.
+/*!
+ * Generic hashing support.
+ *
+ * This module provides a generic way to compute the hash of a value. The
+ * simplest way to make a type hashable is to use `#[deriving(Hash)]`:
+ *
+ * # Example
+ *
+ * ```rust
+ * use std::hash;
+ * use std::hash::Hash;
+ *
+ * #[deriving(Hash)]
+ * struct Person {
+ *     id: uint,
+ *     name: String,
+ *     phone: u64,
+ * }
+ *
+ * let person1 = Person { id: 5, name: "Janet".to_string(), phone: 555_666_7777 };
+ * let person2 = Person { id: 5, name: "Bob".to_string(), phone: 555_666_7777 };
+ *
+ * assert!(hash::hash(&person1) != hash::hash(&person2));
+ * ```
+ *
+ * If you need more control over how a value is hashed, you need to implement
+ * the trait `Hash`:
+ *
+ * ```rust
+ * use std::hash;
+ * use std::hash::Hash;
+ * use std::hash::sip::SipState;
+ *
+ * struct Person {
+ *     id: uint,
+ *     name: String,
+ *     phone: u64,
+ * }
+ *
+ * impl Hash for Person {
+ *     fn hash(&self, state: &mut SipState) {
+ *         self.id.hash(state);
+ *         self.phone.hash(state);
+ *     }
+ * }
+ *
+ * let person1 = Person { id: 5, name: "Janet".to_string(), phone: 555_666_7777 };
+ * let person2 = Person { id: 5, name: "Bob".to_string(), phone: 555_666_7777 };
+ *
+ * assert!(hash::hash(&person1) == hash::hash(&person2));
+ * ```
+ */
 
 pub use core_collections::hash::{Hash, Hasher, Writer, hash, sip};