util/Intrusive*: add C++20 concept checks

src/util/Concepts.hxx

@@ -31,6 +31,20 @@
 
 #include <concepts>
 
+/**
+ * Compatibility wrapper for std::invocable which is unavailable in
+ * the Android NDK r25b and Apple Xcode.
+ */
+#if !defined(ANDROID) && !defined(__APPLE__)
+template<typename F, typename... Args>
+concept Invocable = std::invocable<F, Args...>;
+#else
+template<typename F, typename... Args>
+concept Invocable = requires(F f, Args... args) {
+	{ f(args...) };
+};
+#endif
+
 /**
  * Compatibility wrapper for std::predicate which is unavailable in
  * the Android NDK r25b and Apple Xcode.
@@ -44,3 +58,6 @@ concept Predicate = requires(F f, Args... args) {
 	{ f(args...) } -> std::same_as<bool>;
 };
 #endif
+
+template<typename F, typename T>
+concept Disposer = Invocable<F, T *>;

src/util/IntrusiveForwardList.hxx

@@ -33,6 +33,7 @@
 #pragma once
 
 #include "Cast.hxx"
+#include "Concepts.hxx"
 #include "MemberPointer.hxx"
 #include "OptionalCounter.hxx"
 #include "ShallowCopy.hxx"
@@ -198,8 +199,7 @@ public:
 		counter.reset();
 	}
 
-	template<typename D>
+	void clear_and_dispose(Disposer<value_type> auto disposer) noexcept {
-	void clear_and_dispose(D &&disposer) noexcept {
 		while (!empty()) {
 			auto *item = &front();
 			pop_front();

src/util/IntrusiveHashSet.hxx

@@ -29,6 +29,7 @@
 
 #pragma once
 
+#include "Concepts.hxx"
 #include "IntrusiveList.hxx"
 
 #include <algorithm> // for std::all_of()
@@ -192,15 +193,15 @@ public:
 		counter.reset();
 	}
 
-	template<typename D>
+	constexpr void clear_and_dispose(Disposer<value_type> auto disposer) noexcept {
-	constexpr void clear_and_dispose(D &&disposer) noexcept {
 		for (auto &i : table)
 			i.clear_and_dispose(disposer);
 
 		counter.reset();
 	}
 
-	void remove_and_dispose_if(auto &&pred, auto &&disposer) noexcept {
+	void remove_and_dispose_if(Predicate<const_reference> auto pred,
+				   Disposer<value_type> auto disposer) noexcept {
 		static_assert(!constant_time_size, "Not yet implemented");
 
 		for (auto &bucket : table)
@@ -238,7 +239,7 @@ public:
 	}
 
 	constexpr bucket_iterator erase_and_dispose(bucket_iterator i,
-						    auto &&disposer) noexcept {
+						    Disposer<value_type> auto disposer) noexcept {
 		auto result = erase(i);
 		disposer(&*i);
 		return result;
@@ -272,7 +273,7 @@ public:
 	 */
 	[[nodiscard]] [[gnu::pure]]
 	constexpr bucket_iterator find_if(const auto &key,
-					  auto &&pred) noexcept {
+					  Disposer<value_type> auto pred) noexcept {
 		auto &bucket = GetBucket(key);
 		for (auto &i : bucket)
 			if (equal(key, i) && pred(i))

src/util/IntrusiveList.hxx

@@ -30,6 +30,7 @@
 #pragma once
 
 #include "Cast.hxx"
+#include "Concepts.hxx"
 #include "IntrusiveHookMode.hxx"
 #include "MemberPointer.hxx"
 #include "OptionalCounter.hxx"
@@ -287,8 +288,7 @@ public:
 		}
 	}
 
-	template<typename D>
+	void clear_and_dispose(Disposer<value_type> auto disposer) noexcept {
-	void clear_and_dispose(D &&disposer) noexcept {
 		while (!empty()) {
 			auto *item = &front();
 			pop_front();
@@ -296,8 +296,8 @@ public:
 		}
 	}
 
-	template<typename P, typename D>
+	void remove_and_dispose_if(Predicate<const_reference> auto pred,
-	void remove_and_dispose_if(P &&pred, D &&dispose) noexcept {
+				   Disposer<value_type> auto dispose) noexcept {
 		auto *n = head.next;
 
 		while (n != &head) {
@@ -325,8 +325,7 @@ public:
 		--counter;
 	}
 
-	template<typename D>
+	void pop_front_and_dispose(Disposer<value_type> auto disposer) noexcept {
-	void pop_front_and_dispose(D &&disposer) noexcept {
 		auto &i = front();
 		ToHook(i).unlink();
 		--counter;
@@ -479,8 +478,8 @@ public:
 		return result;
 	}
 
-	template<typename D>
+	iterator erase_and_dispose(iterator i,
-	iterator erase_and_dispose(iterator i, D &&disposer) noexcept {
+				   Disposer<value_type> auto disposer) noexcept {
 		auto result = erase(i);
 		disposer(&*i);
 		return result;