Merge pull request #16 from dtolnay/order

Add preserve_order feature to use LinkedHashMap instead of BTreeMap

Cargo.toml

@@ -8,5 +8,9 @@ license = "MIT/Apache-2.0"
 description = "The missing YAML 1.2 parser for rust"
 repository = "https://github.com/chyh1990/yaml-rust"
 
+[features]
+preserve_order = ["linked-hash-map"]
+
 [dependencies]
 clippy = { version = "^0.*", optional = true }
+linked-hash-map = { version = "0.0.9", optional = true }

src/lib.rs

@@ -42,6 +42,9 @@
 #![cfg_attr(feature="clippy", warn(cyclomatic_complexity))]
 #![cfg_attr(feature="clippy", allow(match_same_arms))]
 
+#[cfg(feature = "preserve_order")]
+extern crate linked_hash_map;
+
 pub mod yaml;
 pub mod scanner;
 pub mod parser;

src/yaml.rs

@@ -23,7 +23,7 @@ use scanner::{TScalarStyle, ScanError, TokenType};
 ///     assert!(v.as_i64().is_some());
 /// }
 /// ```
-#[derive(Clone, PartialEq, PartialOrd, Debug, Eq, Ord)]
+#[derive(Clone, PartialEq, PartialOrd, Debug, Eq, Ord, Hash)]
 pub enum Yaml {
     /// Float types are stored as String and parsed on demand.
     /// Note that f64 does NOT implement Eq trait and can NOT be stored in BTreeMap.
@@ -37,6 +37,15 @@ pub enum Yaml {
     /// YAML array, can be accessed as a `Vec`.
     Array(self::Array),
     /// YAML hash, can be accessed as a `BTreeMap`.
+    ///
+    /// If the order of keys is meaningful, enable the `preserve_order` feature to
+    /// store hashes as a `LinkedHashMap` intead of `BTreeMap`. When using a
+    /// `LinkedHashMap`, the itertion order will match the order of insertion into
+    /// the map.
+    ///
+    /// ```toml
+    /// yaml-rust = { version = "*", features = ["preserve_order"] }
+    /// ```
     Hash(self::Hash),
     /// Alias, not fully supported yet.
     Alias(usize),
@@ -49,7 +58,11 @@ pub enum Yaml {
 }
 
 pub type Array = Vec<Yaml>;
+
+#[cfg(not(feature = "preserve_order"))]
 pub type Hash = BTreeMap<Yaml, Yaml>;
+#[cfg(feature = "preserve_order")]
+pub type Hash = ::linked_hash_map::LinkedHashMap<Yaml, Yaml>;
 
 pub struct YamlLoader {
     docs: Vec<Yaml>,