From 0dc4929c5e3f5b6cd7ff767993f2c86eb2f531a5 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Tue, 18 Feb 2020 11:23:21 +1100
Subject: [PATCH] concepts: add initial testing header

---
 CMakeLists.txt    |   2 +
 concepts.hpp      | 168 ++++++++++++++++++++++++++++++++++++++++++++++
 test/concepts.cpp |  12 ++++
 3 files changed, 182 insertions(+)
 create mode 100644 concepts.hpp
 create mode 100644 test/concepts.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e43cd359..a08c8632 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -288,6 +288,7 @@ list (
     cmdopt.hpp
     colour.cpp
     colour.hpp
+    concepts.hpp
     container.hpp
     coord.hpp
     coord/fwd.hpp
@@ -660,6 +661,7 @@ if (TESTS)
         buffer/simple
         cmdopt
         colour
+        concepts
         comparator
         coord
         encode/number
diff --git a/concepts.hpp b/concepts.hpp
new file mode 100644
index 00000000..acb0db19
--- /dev/null
+++ b/concepts.hpp
@@ -0,0 +1,168 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 2020, Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+#include <type_traits>
+#include <utility>
+
+
+///////////////////////////////////////////////////////////////////////////////
+/// A minimal implementation of the standard concept library for use with
+/// compilers that lack it.
+///
+/// Portions of this code are adapted from the standard and as such do not
+/// fall under the top copyright notice.
+///
+/// clang#xxx: Remove me when clang includes an implementation of these.
+namespace cruft::concepts {
+    template <class T>
+    concept default_constructible = std::is_default_constructible_v<T>;
+
+    template <class T>
+    concept copy_constructible = std::is_copy_constructible_v<T>;
+
+    template <class T>
+    concept move_constructible = std::is_move_constructible_v<T>;
+
+    template <typename T>
+    concept destructible = std::is_nothrow_destructible_v<T>;
+
+
+    template <typename A, typename B>
+    concept same_as = std::is_same_v<A, B> and std::is_same_v<B, A>;
+
+
+    template <typename From, typename To>
+    concept convertible_to =
+        std::is_convertible_v<From, To> &&
+        requires (From (&f)())
+    {
+        static_cast<To> (f());
+    };
+
+
+    template <
+        typename LHS,
+        typename RHS
+    >
+    concept assignable_from =
+        std::is_lvalue_reference_v<LHS> &&
+        // clang#xxx: common_reference_t is too annoying to implement as
+        // a temporary fix for this temporary fix. Reintroduce this when
+        // clang knows about common_reference_t.
+        // std::common_reference_with<
+        //     std::remove_reference_t<LHS> const&,
+        //     std::remove_reference_t<RHS> const&
+        // > &&
+        requires(LHS lhs, RHS&& rhs)
+    {
+        { lhs = std::forward<RHS>(rhs) } -> same_as<LHS>;
+    };
+
+
+    template <typename T>
+    concept swappable = requires (T &&a, T &&b) { swap (a, b); };
+
+
+    template < class T >
+    concept movable =
+      std::is_object_v<T> &&
+      move_constructible<T> &&
+      assignable_from<T&, T> &&
+      swappable<T>;
+
+
+    template <typename T>
+    concept boolean =
+        movable<std::remove_cvref_t<T>> &&
+        requires (
+            std::remove_reference_t<T> const& b1,
+            std::remove_reference_t<T> const& b2,
+            bool const a
+        )
+    {
+        {  b1 } -> convertible_to<bool>;
+        { !b1 } -> convertible_to<bool>;
+
+        { b1 && b2 } -> same_as<bool>;
+        { b1 &&  a } -> same_as<bool>;
+        {  a && b2 } -> same_as<bool>;
+        { b1 || b2 } -> same_as<bool>;
+        { b1 ||  a } -> same_as<bool>;
+        {  a || b2 } -> same_as<bool>;
+
+        { b1 == b2 } -> convertible_to<bool>;
+        { b1 ==  a } -> convertible_to<bool>;
+        {  a == b2 } -> convertible_to<bool>;
+        { b1 != b2 } -> convertible_to<bool>;
+        { b1 !=  a } -> convertible_to<bool>;
+        {  a != b2 } -> convertible_to<bool>;
+    };
+
+
+    template <typename T>
+    concept equality_comparable =
+        requires (
+            std::remove_reference_t<T> const &a,
+            std::remove_reference_t<T> const &b
+        )
+    {
+        { a == b } -> boolean;
+        { a != b } -> boolean;
+        { b == a } -> boolean;
+        { b != a } -> boolean;
+    };
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+// C++ named requirements
+namespace cruft::concepts {
+    /// Corresponds to the "Container" named requirement.
+    template <class T>
+    concept container =
+        default_constructible<T> &&
+        copy_constructible<T> &&
+        move_constructible<T> &&
+        destructible<T> &&
+        equality_comparable<T> &&
+        requires (T a, T b)
+    {
+        typename T::value_type;
+        typename T::reference;
+        typename T::const_reference;
+        typename T::iterator;
+        typename T::const_iterator;
+        typename T::difference_type;
+        typename T::size_type;
+
+        { a = b } -> same_as<T&>;
+        { a = std::move (b) } -> same_as<T&>;
+
+        { a.begin  () } -> same_as<typename T::iterator>;
+        { a.end    () } -> same_as<typename T::iterator>;
+        { a.cbegin () } -> same_as<typename T::const_iterator>;
+        { a.cend   () } -> same_as<typename T::const_iterator>;
+
+        { a.swap (b)  } -> same_as<void>;
+        { swap (a, b) } -> same_as<void>;
+
+        { a.size () } -> same_as<typename T::size_type>;
+        { a.max_size () } -> same_as<typename T::size_type>;
+        { a.empty () } -> boolean;
+    };
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+// Some handy non-standard concepts
+namespace cruft::concepts {
+    template <class T>
+    concept arithmetic = std::is_arithmetic_v<T>;
+}
diff --git a/test/concepts.cpp b/test/concepts.cpp
new file mode 100644
index 00000000..5dd4d72a
--- /dev/null
+++ b/test/concepts.cpp
@@ -0,0 +1,12 @@
+#include <cruft/util/tap.hpp>
+#include <cruft/util/concepts.hpp>
+
+int main ()
+{
+    cruft::TAP::logger tap;
+
+    tap.expect (cruft::concepts::container<std::vector<int>>, "vector is a container");
+    tap.expect (!cruft::concepts::container<int>, "int is not a container");
+
+    return tap.status ();
+}
\ No newline at end of file