From dca03e5e3645b088a01446b2ed71b51eb7f7b493 Mon Sep 17 00:00:00 2001
From: Goober5000 <ipw47@mailbox.org>
Date: Wed, 12 Nov 2025 21:48:34 -0500
Subject: [PATCH] configurable sets

Add the ability to configure the `less` operator for `SCP_set`, `SCP_map`, and so forth.  Add an `ID_Less` functor so that the type-safe `ID` class can be used with these data structures.
---
 code/globalincs/vmallocator.h | 20 ++++++++++----------
 code/utils/id.h               |  9 +++++++++
 2 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/code/globalincs/vmallocator.h b/code/globalincs/vmallocator.h
index 191e0771007..131fddbdf09 100644
--- a/code/globalincs/vmallocator.h
+++ b/code/globalincs/vmallocator.h
@@ -97,11 +97,11 @@ extern bool lcase_equal(const SCP_string& _Left, const SCP_string& _Right);
 extern bool lcase_lessthan(const SCP_string& _Left, const SCP_string& _Right);
 
 
-template <typename T, typename U>
-using SCP_map = std::map<T, U, std::less<T>, std::allocator<std::pair<const T, U>>>;
+template <typename T, typename U, typename Less = std::less<T>>
+using SCP_map = std::map<T, U, Less, std::allocator<std::pair<const T, U>>>;
 
-template <typename T, typename U>
-using SCP_multimap = std::multimap<T, U, std::less<T>, std::allocator<std::pair<const T, U>>>;
+template <typename T, typename U, typename Less = std::less<T>>
+using SCP_multimap = std::multimap<T, U, Less, std::allocator<std::pair<const T, U>>>;
 
 template <typename T>
 using SCP_queue = std::queue<T, std::deque<T, std::allocator<T>>>;
@@ -109,11 +109,11 @@ using SCP_queue = std::queue<T, std::deque<T, std::allocator<T>>>;
 template <typename T>
 using SCP_deque = std::deque<T, std::allocator<T>>;
 
-template <typename T>
-class SCP_set : public std::set<T, std::less<T>, std::allocator<T>>
+template <typename T, typename Less = std::less<T>>
+class SCP_set : public std::set<T, Less, std::allocator<T>>
 {
 public:
-	using std::set<T, std::less<T>, std::allocator<T>>::set;	// inherit all constructors
+	using std::set<T, Less, std::allocator<T>>::set;	// inherit all constructors
 
 	bool contains(const T& item) const
 	{
@@ -121,11 +121,11 @@ class SCP_set : public std::set<T, std::less<T>, std::allocator<T>>
 	}
 };
 
-template <typename T>
-class SCP_multiset : public std::multiset<T, std::less<T>, std::allocator<T>>
+template <typename T, typename Less = std::less<T>>
+class SCP_multiset : public std::multiset<T, Less, std::allocator<T>>
 {
 public:
-	using std::multiset<T, std::less<T>, std::allocator<T>>::multiset;	// inherit all constructors
+	using std::multiset<T, Less, std::allocator<T>>::multiset;	// inherit all constructors
 
 	bool contains(const T& item) const
 	{
diff --git a/code/utils/id.h b/code/utils/id.h
index fd66f561ab8..37915029d33 100644
--- a/code/utils/id.h
+++ b/code/utils/id.h
@@ -61,4 +61,13 @@ struct ID_Hash
 	}
 };
 
+struct ID_Less
+{
+	template <class Tag, class Impl, Impl default_value>
+	bool operator()(const ID<Tag, Impl, default_value> &lhs, const ID<Tag, Impl, default_value> &rhs) const
+	{
+		return std::less<Impl>{}(lhs.value(), rhs.value());
+	}
+};
+
 }