From c8bee92fb9ae1479077071cd5ffed58be77d0b26 Mon Sep 17 00:00:00 2001
From: Hendiadyoin1 <leon2002.la@gmail.com>
Date: Sun, 7 Nov 2021 14:50:41 +0100
Subject: [PATCH] AK: Add the concept of hash-compatible types

---
 AK/Concepts.h           | 3 +++
 AK/StdLibExtraDetails.h | 7 +++++++
 AK/StringUtils.h        | 6 ++++++
 3 files changed, 16 insertions(+)

diff --git a/AK/Concepts.h b/AK/Concepts.h
index 2996e43633b..00580face5f 100644
--- a/AK/Concepts.h
+++ b/AK/Concepts.h
@@ -36,6 +36,9 @@ concept SameAs = IsSame<T, U>;
 template<typename T>
 concept AnyString = Detail::IsConstructible<StringView, T>;
 
+template<typename T, typename U>
+concept HashCompatible = IsHashCompatible<Detail::Decay<T>, Detail::Decay<U>>;
+
 // FIXME: remove once Clang formats these properly.
 // clang-format off
 template<typename Func, typename... Args>
diff --git a/AK/StdLibExtraDetails.h b/AK/StdLibExtraDetails.h
index 0235022f04a..1b91e337516 100644
--- a/AK/StdLibExtraDetails.h
+++ b/AK/StdLibExtraDetails.h
@@ -575,6 +575,12 @@ using Decay = typename __decay<T>::type;
 
 template<typename T, typename U>
 inline constexpr bool IsPointerOfType = IsPointer<Decay<U>>&& IsSame<T, RemoveCV<RemovePointer<Decay<U>>>>;
+
+template<typename T, typename U>
+inline constexpr bool IsHashCompatible = false;
+template<typename T>
+inline constexpr bool IsHashCompatible<T, T> = true;
+
 }
 using AK::Detail::AddConst;
 using AK::Detail::AddLvalueReference;
@@ -605,6 +611,7 @@ using AK::Detail::IsEnum;
 using AK::Detail::IsFloatingPoint;
 using AK::Detail::IsFunction;
 using AK::Detail::IsFundamental;
+using AK::Detail::IsHashCompatible;
 using AK::Detail::IsIntegral;
 using AK::Detail::IsLvalueReference;
 using AK::Detail::IsMoveAssignable;
diff --git a/AK/StringUtils.h b/AK/StringUtils.h
index 13794c4d0c9..ca079cb82ad 100644
--- a/AK/StringUtils.h
+++ b/AK/StringUtils.h
@@ -7,10 +7,16 @@
 
 #pragma once
 
+#include <AK/Concepts.h>
 #include <AK/Forward.h>
 
 namespace AK {
 
+namespace Detail {
+template<Concepts::AnyString T, Concepts::AnyString U>
+inline constexpr bool IsHashCompatible<T, U> = true;
+}
+
 enum class CaseSensitivity {
     CaseInsensitive,
     CaseSensitive,