add rustc_hash as a feature-gated dependency

Author: knickish

Cargo.toml

@@ -10,6 +10,7 @@ categories    = ["compression"]
 
 [dependencies]
 nanoserde           = { version = "^0.1.37", optional = true }
+rustc-hash          = { version = "1.1.0", optional = true }
 serde               = { version = "^1.0.0", optional = true, features = ["derive"] }
 structdiff-derive   = { path = "derive", version = "=0.6.1" }
 
@@ -19,6 +20,7 @@ structdiff-derive   = { path = "derive", version = "=0.6.1" }
 "serde"         = ["dep:serde", "structdiff-derive/serde"]
 "debug_diffs"   = ["structdiff-derive/debug_diffs"]
 "generated_setters" = ["structdiff-derive/generated_setters"]
+"rustc_hash"    = ["dep:rustc-hash"]
 "debug_asserts" = []
 
 [dev-dependencies]

README.md

@@ -65,6 +65,7 @@ For more examples take a look at [integration tests](/tests)
 - [`nanoserde`, `serde`] - Serialization of `Difference` derived associated types. Allows diffs to easily be sent over network.
 - `debug_diffs` - Derive `Debug` on the generated diff type
 - `generated_setters` - Enable generation of setters for struct fields. These setters automatically return a diff if a field's value is changed by the assignment.
+- `rustc_hash` - Use the (non-cryptographic) hash implementation from the `rustc-hash` crate instead of the default hasher. Much faster diff generation for collections at the cost of a dependency.
 
 ### Development status 
 This is being used actively for my own projects, although it's mostly working now. PRs will be accepted for either more tests or functionality.

src/collections/unordered_array_like.rs

@@ -2,7 +2,13 @@
 use nanoserde::{DeBin, SerBin};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
-use std::{collections::HashMap, hash::Hash};
+#[cfg(not(feature = "rustc_hash"))]
+type HashMap<K, V> = std::collections::HashMap<K, V>;
+#[cfg(feature = "rustc_hash")]
+type HashMap<K, V> =
+    std::collections::HashMap<K, V, std::hash::BuildHasherDefault<rustc_hash::FxHasher>>;
+
+use std::hash::Hash;
 
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -88,7 +94,9 @@ impl<'a, T: Clone + 'a> From<UnorderedArrayLikeDiff<&'a T>> for UnorderedArrayLi
 fn collect_into_map<'a, T: Hash + PartialEq + Eq + 'a, B: Iterator<Item = T>>(
     list: B,
 ) -> HashMap<T, usize> {
-    let mut map: HashMap<T, usize> = HashMap::with_capacity(list.size_hint().1.unwrap_or_default());
+    let mut map: HashMap<T, usize> = HashMap::default();
+    map.reserve(list.size_hint().1.unwrap_or_default());
+
     for item in list {
         match map.get_mut(&item) {
             Some(count) => *count += 1,

src/collections/unordered_map_like.rs

@@ -2,7 +2,13 @@
 use nanoserde::{DeBin, SerBin};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
-use std::{collections::HashMap, hash::Hash};
+#[cfg(not(feature = "rustc_hash"))]
+type HashMap<K, V> = std::collections::HashMap<K, V>;
+#[cfg(feature = "rustc_hash")]
+type HashMap<K, V> =
+    std::collections::HashMap<K, V, std::hash::BuildHasherDefault<rustc_hash::FxHasher>>;
+
+use std::hash::Hash;
 
 #[derive(Debug, Clone)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -111,8 +117,8 @@ fn collect_into_key_eq_map<
 >(
     list: B,
 ) -> HashMap<&'a K, (&'a V, usize)> {
-    let mut map: HashMap<&K, (&V, usize)> =
-        HashMap::with_capacity(list.size_hint().1.unwrap_or_default());
+    let mut map: HashMap<&K, (&V, usize)> = HashMap::default();
+    map.reserve(list.size_hint().1.unwrap_or_default());
     for (key, value) in list {
         match map.get_mut(&key) {
             Some((_, count)) => *count += 1,
@@ -132,7 +138,9 @@ fn collect_into_key_value_eq_map<
 >(
     list: B,
 ) -> HashMap<&'a K, (&'a V, usize)> {
-    let mut map: HashMap<&K, (&V, usize)> = HashMap::new();
+    let mut map: HashMap<&K, (&V, usize)> = HashMap::default();
+    map.reserve(list.size_hint().1.unwrap_or_default());
+
     for (key, value) in list {
         match map.get_mut(&key) {
             Some((ref current_val, count)) => match current_val == &value {

src/collections/unordered_map_like_recursive.rs

@@ -5,7 +5,13 @@ use serde::{Deserialize, Serialize};
 #[cfg(feature = "debug_diffs")]
 use std::fmt::Debug;
 
-use std::{collections::HashMap, hash::Hash, marker::PhantomData};
+#[cfg(not(feature = "rustc_hash"))]
+type HashMap<K, V> = std::collections::HashMap<K, V>;
+#[cfg(feature = "rustc_hash")]
+type HashMap<K, V> =
+    std::collections::HashMap<K, V, std::hash::BuildHasherDefault<rustc_hash::FxHasher>>;
+
+use std::{hash::Hash, marker::PhantomData};
 
 use crate::StructDiff;
 
@@ -110,7 +116,9 @@ fn collect_into_key_eq_map<
 >(
     list: B,
 ) -> HashMap<&'a K, &'a V> {
-    let mut map: HashMap<&K, &V> = HashMap::with_capacity(list.size_hint().1.unwrap_or_default());
+    let mut map: HashMap<&K, &V> = HashMap::default();
+    map.reserve(list.size_hint().1.unwrap_or_default());
+
     for (key, value) in list {
         map.insert(key, value);
     }