AK: Support case-insensitive HashMap<String, T>.

We achieve this by allowing you to specify custom traits for the key type.
For convenience, we also provide a CaseInsensitiveStringTraits for String.

AK/AKString.h

@@ -219,6 +219,12 @@ struct Traits<String> : public GenericTraits<String> {
     static void dump(const String& s) { kprintf("%s", s.characters()); }
 };
 
+struct CaseInsensitiveStringTraits : public AK::Traits<String> {
+    static unsigned hash(const String& s) { return s.impl() ? s.to_lowercase().impl()->hash() : 0; }
+    static bool equals(const String& a, const String& b) { return a.to_lowercase() == b.to_lowercase(); }
+
+};
+
 inline bool operator<(const char* characters, const String& string)
 {
     if (!characters)
@@ -254,3 +260,4 @@ inline bool operator<=(const char* characters, const String& string)
 }
 
 using AK::String;
+using AK::CaseInsensitiveStringTraits;

AK/HashMap.h

@@ -7,7 +7,7 @@
 
 namespace AK {
 
-template<typename K, typename V>
+template<typename K, typename V, typename KeyTraits = Traits<K>>
 class HashMap {
 private:
     struct Entry {
@@ -16,12 +16,12 @@ private:
     };
 
     struct EntryTraits {
-        static unsigned hash(const Entry& entry) { return Traits<K>::hash(entry.key); }
-        static bool equals(const Entry& a, const Entry& b) { return a.key == b.key; }
+        static unsigned hash(const Entry& entry) { return KeyTraits::hash(entry.key); }
+        static bool equals(const Entry& a, const Entry& b) { return KeyTraits::equals(a.key, b.key); }
         static void dump(const Entry& entry)
         {
             kprintf("key=");
-            Traits<K>::dump(entry.key);
+            KeyTraits::dump(entry.key);
             kprintf(" value=");
             Traits<V>::dump(entry.value);
         }
@@ -51,11 +51,11 @@ public:
 
     IteratorType begin() { return m_table.begin(); }
     IteratorType end() { return m_table.end(); }
-    IteratorType find(const K& key) { return m_table.find(Traits<K>::hash(key), [&](auto& entry) { return key == entry.key; }); }
+    IteratorType find(const K& key) { return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); }); }
 
     ConstIteratorType begin() const { return m_table.begin(); }
     ConstIteratorType end() const { return m_table.end(); }
-    ConstIteratorType find(const K& key) const { return m_table.find(Traits<K>::hash(key), [&](auto& entry) { return key == entry.key; }); }
+    ConstIteratorType find(const K& key) const { return m_table.find(KeyTraits::hash(key), [&](auto& entry) { return KeyTraits::equals(key, entry.key); }); }
 
     void ensure_capacity(int capacity) { m_table.ensure_capacity(capacity); }
 

AK/Tests/TestHashMap.cpp

@@ -32,5 +32,14 @@ int main()
     EXPECT(number_to_string.find(3) == number_to_string.end());
 
     EXPECT_EQ(loop_counter, 3);
+
+    {
+        HashMap<String, int, CaseInsensitiveStringTraits> casemap;
+        EXPECT_EQ(String("nickserv").to_lowercase(), String("NickServ").to_lowercase());
+        casemap.set("nickserv", 3);
+        casemap.set("NickServ", 3);
+        EXPECT_EQ(casemap.size(), 1);
+    }
+
     return 0;
 }