Checked: constexpr support

Problem:
- `Checked` is not `constexpr`-aware.

Solution:
- Decorate member functions with `constexpr` keyword.
- Add tests to ensure the functionality where possible.

AK/Checked.h

@@ -112,111 +112,111 @@ inline constexpr bool is_within_range(Source value)
 template<typename T>
 class Checked {
 public:
-    Checked() = default;
+    constexpr Checked() = default;
 
-    Checked(T value)
+    constexpr Checked(T value)
         : m_value(value)
     {
     }
 
     template<typename U>
-    Checked(U value)
+    constexpr Checked(U value)
     {
         m_overflow = !is_within_range<T>(value);
         m_value = value;
     }
 
-    Checked(const Checked&) = default;
+    constexpr Checked(const Checked&) = default;
 
-    Checked(Checked&& other)
+    constexpr Checked(Checked&& other)
         : m_value(exchange(other.m_value, 0))
         , m_overflow(exchange(other.m_overflow, false))
     {
     }
 
     template<typename U>
-    Checked& operator=(U value)
+    constexpr Checked& operator=(U value)
     {
         return *this = Checked(value);
     }
 
-    Checked& operator=(const Checked& other) = default;
+    constexpr Checked& operator=(const Checked& other) = default;
 
-    Checked& operator=(Checked&& other)
+    constexpr Checked& operator=(Checked&& other)
     {
         m_value = exchange(other.m_value, 0);
         m_overflow = exchange(other.m_overflow, false);
         return *this;
     }
 
-    bool has_overflow() const
+    constexpr bool has_overflow() const
     {
         return m_overflow;
     }
 
-    ALWAYS_INLINE bool operator!() const
+    ALWAYS_INLINE constexpr bool operator!() const
     {
         ASSERT(!m_overflow);
         return !m_value;
     }
 
-    ALWAYS_INLINE T value() const
+    ALWAYS_INLINE constexpr T value() const
     {
         ASSERT(!m_overflow);
         return m_value;
     }
 
-    void add(T other)
+    constexpr void add(T other)
     {
         m_overflow |= __builtin_add_overflow(m_value, other, &m_value);
     }
 
-    void sub(T other)
+    constexpr void sub(T other)
     {
         m_overflow |= __builtin_sub_overflow(m_value, other, &m_value);
     }
 
-    void mul(T other)
+    constexpr void mul(T other)
     {
         m_overflow |= __builtin_mul_overflow(m_value, other, &m_value);
     }
 
-    void div(T other)
+    constexpr void div(T other)
     {
         m_value /= other;
     }
 
-    Checked& operator+=(T other)
+    constexpr Checked& operator+=(T other)
     {
         add(other);
         return *this;
     }
 
-    Checked& operator-=(T other)
+    constexpr Checked& operator-=(T other)
     {
         sub(other);
         return *this;
     }
 
-    Checked& operator*=(T other)
+    constexpr Checked& operator*=(T other)
     {
         mul(other);
         return *this;
     }
 
-    Checked& operator/=(T other)
+    constexpr Checked& operator/=(T other)
     {
         div(other);
         return *this;
     }
 
-    Checked& operator++()
+    constexpr Checked& operator++()
     {
         add(1);
         return *this;
     }
 
-    Checked operator++(int)
+    constexpr Checked operator++(int)
     {
         Checked old { *this };
         add(1);
@@ -224,7 +224,7 @@ public:
     }
 
     template<typename U, typename V>
-    static bool addition_would_overflow(U u, V v)
+    static constexpr bool addition_would_overflow(U u, V v)
     {
 #ifdef __clang__
         Checked checked;
@@ -237,7 +237,7 @@ public:
     }
 
     template<typename U, typename V>
-    static bool multiplication_would_overflow(U u, V v)
+    static constexpr bool multiplication_would_overflow(U u, V v)
     {
 #ifdef __clang__
         Checked checked;
@@ -250,7 +250,7 @@ public:
     }
 
     template<typename U, typename V, typename X>
-    static bool multiplication_would_overflow(U u, V v, X x)
+    static constexpr bool multiplication_would_overflow(U u, V v, X x)
     {
         Checked checked;
         checked = u;
@@ -265,7 +265,7 @@ private:
 };
 
 template<typename T>
-inline Checked<T> operator+(const Checked<T>& a, const Checked<T>& b)
+constexpr Checked<T> operator+(const Checked<T>& a, const Checked<T>& b)
 {
     Checked<T> c { a };
     c.add(b.value());
@@ -273,7 +273,7 @@ inline Checked<T> operator+(const Checked<T>& a, const Checked<T>& b)
 }
 
 template<typename T>
-inline Checked<T> operator-(const Checked<T>& a, const Checked<T>& b)
+constexpr Checked<T> operator-(const Checked<T>& a, const Checked<T>& b)
 {
     Checked<T> c { a };
     c.sub(b.value());
@@ -281,7 +281,7 @@ inline Checked<T> operator-(const Checked<T>& a, const Checked<T>& b)
 }
 
 template<typename T>
-inline Checked<T> operator*(const Checked<T>& a, const Checked<T>& b)
+constexpr Checked<T> operator*(const Checked<T>& a, const Checked<T>& b)
 {
     Checked<T> c { a };
     c.mul(b.value());
@@ -289,7 +289,7 @@ inline Checked<T> operator*(const Checked<T>& a, const Checked<T>& b)
 }
 
 template<typename T>
-inline Checked<T> operator/(const Checked<T>& a, const Checked<T>& b)
+constexpr inline Checked<T> operator/(const Checked<T>& a, const Checked<T>& b)
 {
     Checked<T> c { a };
     c.div(b.value());
@@ -297,79 +297,79 @@ inline Checked<T> operator/(const Checked<T>& a, const Checked<T>& b)
 }
 
 template<typename T>
-inline bool operator<(const Checked<T>& a, T b)
+constexpr bool operator<(const Checked<T>& a, T b)
 {
     return a.value() < b;
 }
 
 template<typename T>
-inline bool operator>(const Checked<T>& a, T b)
+constexpr bool operator>(const Checked<T>& a, T b)
 {
     return a.value() > b;
 }
 
 template<typename T>
-inline bool operator>=(const Checked<T>& a, T b)
+constexpr bool operator>=(const Checked<T>& a, T b)
 {
     return a.value() >= b;
 }
 
 template<typename T>
-inline bool operator<=(const Checked<T>& a, T b)
+constexpr bool operator<=(const Checked<T>& a, T b)
 {
     return a.value() <= b;
 }
 
 template<typename T>
-inline bool operator==(const Checked<T>& a, T b)
+constexpr bool operator==(const Checked<T>& a, T b)
 {
     return a.value() == b;
 }
 
 template<typename T>
-inline bool operator!=(const Checked<T>& a, T b)
+constexpr bool operator!=(const Checked<T>& a, T b)
 {
     return a.value() != b;
 }
 
 template<typename T>
-inline bool operator<(T a, const Checked<T>& b)
+constexpr bool operator<(T a, const Checked<T>& b)
 {
     return a < b.value();
 }
 
 template<typename T>
-inline bool operator>(T a, const Checked<T>& b)
+constexpr bool operator>(T a, const Checked<T>& b)
 {
     return a > b.value();
 }
 
 template<typename T>
-inline bool operator>=(T a, const Checked<T>& b)
+constexpr bool operator>=(T a, const Checked<T>& b)
 {
     return a >= b.value();
 }
 
 template<typename T>
-inline bool operator<=(T a, const Checked<T>& b)
+constexpr bool operator<=(T a, const Checked<T>& b)
 {
     return a <= b.value();
 }
 
 template<typename T>
-inline bool operator==(T a, const Checked<T>& b)
+constexpr bool operator==(T a, const Checked<T>& b)
 {
     return a == b.value();
 }
 
 template<typename T>
-inline bool operator!=(T a, const Checked<T>& b)
+constexpr bool operator!=(T a, const Checked<T>& b)
 {
     return a != b.value();
 }
 
 template<typename T>
-inline Checked<T> make_checked(T value)
+constexpr Checked<T> make_checked(T value)
 {
     return Checked<T>(value);
 }

AK/StdLibExtras.h

@@ -82,7 +82,7 @@ inline constexpr T ceil_div(T a, U b)
 #    pragma clang diagnostic ignored "-Wconsumed"
 #endif
 template<typename T>
-inline T&& move(T& arg)
+constexpr T&& move(T& arg)
 {
     return static_cast<T&&>(arg);
 }
@@ -433,7 +433,7 @@ struct IsConst<const T> : TrueType {
 };
 
 template<typename T, typename U = T>
-inline constexpr T exchange(T& slot, U&& value)
+constexpr T exchange(T& slot, U&& value)
 {
     T old_value = move(slot);
     slot = forward<U>(value);

AK/Tests/TestChecked.cpp

@@ -27,6 +27,7 @@
 #include <AK/TestSuite.h>
 
 #include <AK/Checked.h>
+#include <AK/NumericLimits.h>
 
 // These tests only check whether the usual operator semantics work.
 // TODO: Add tests about the actual `Check`ing itself!
@@ -94,4 +95,272 @@ TEST_CASE(operator_arith)
     EXPECT_EQ(b / a, 28);
 }
 
+TEST_CASE(should_constexpr_default_construct)
+{
+    constexpr Checked<int> checked_value {};
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == int {});
+}
+
+TEST_CASE(should_constexpr_value_construct)
+{
+    constexpr Checked<int> checked_value { 42 };
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_convert_construct)
+{
+    constexpr Checked<int> checked_value { 42u };
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_copy_construct)
+{
+    constexpr auto checked_value = [] {
+        const Checked<int> old_value { 42 };
+        Checked<int> value(old_value);
+        return value;
+    }();
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_move_construct)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value(Checked<int> { 42 });
+        return value;
+    }();
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_copy_assign)
+{
+    constexpr auto checked_value = [] {
+        const Checked<int> old_value { 42 };
+        Checked<int> value {};
+        value = old_value;
+        return value;
+    }();
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_move_assign)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value {};
+        value = Checked<int> { 42 };
+        return value;
+    }();
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_convert_and_assign)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value {};
+        value = 42;
+        return value;
+    }();
+    static_assert(!checked_value.has_overflow());
+    static_assert(checked_value == 42);
+}
+
+TEST_CASE(should_constexpr_not_operator)
+{
+    constexpr Checked<int> value {};
+    static_assert(!value);
+}
+
+TEST_CASE(should_constexpr_value_accessor)
+{
+    constexpr Checked<int> value { 42 };
+    static_assert(value.value() == 42);
+}
+
+TEST_CASE(should_constexpr_add)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value.add(3);
+        return value;
+    }();
+    static_assert(checked_value == 45);
+}
+
+TEST_CASE(should_constexpr_sub)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value.sub(3);
+        return value;
+    }();
+    static_assert(checked_value == 39);
+}
+
+TEST_CASE(should_constexpr_mul)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value.mul(2);
+        return value;
+    }();
+    static_assert(checked_value == 84);
+}
+
+TEST_CASE(should_constexpr_div)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value.div(3);
+        return value;
+    }();
+    static_assert(checked_value == 14);
+}
+
+TEST_CASE(should_constexpr_assignment_by_sum)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value += 3;
+        return value;
+    }();
+    static_assert(checked_value == 45);
+}
+
+TEST_CASE(should_constexpr_assignment_by_diff)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value -= 3;
+        return value;
+    }();
+    static_assert(checked_value == 39);
+}
+
+TEST_CASE(should_constexpr_assignment_by_product)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value *= 2;
+        return value;
+    }();
+    static_assert(checked_value == 84);
+}
+
+TEST_CASE(should_constexpr_assignment_by_quotient)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value /= 3;
+        return value;
+    }();
+    static_assert(checked_value == 14);
+}
+
+TEST_CASE(should_constexpr_prefix_increment)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        ++value;
+        return value;
+    }();
+    static_assert(checked_value == 43);
+}
+
+TEST_CASE(should_constexpr_postfix_increment)
+{
+    constexpr auto checked_value = [] {
+        Checked<int> value { 42 };
+        value++;
+        return value;
+    }();
+    static_assert(checked_value == 43);
+}
+
+TEST_CASE(should_constexpr_check_for_overflow_addition)
+{
+    static_assert(Checked<int>::addition_would_overflow(NumericLimits<int>::max(), 1));
+}
+
+TEST_CASE(should_constexpr_check_for_overflow_multiplication)
+{
+    static_assert(Checked<int>::multiplication_would_overflow(NumericLimits<int>::max(), 2));
+    static_assert(Checked<int>::multiplication_would_overflow(NumericLimits<int>::max(), 1, 2));
+}
+
+TEST_CASE(should_constexpr_add_checked_values)
+{
+    constexpr Checked<int> a { 42 };
+    constexpr Checked<int> b { 17 };
+    constexpr Checked<int> expected { 59 };
+    static_assert(expected == (a + b).value());
+}
+
+TEST_CASE(should_constexpr_subtract_checked_values)
+{
+    constexpr Checked<int> a { 42 };
+    constexpr Checked<int> b { 17 };
+    constexpr Checked<int> expected { 25 };
+    static_assert(expected == (a - b).value());
+}
+
+TEST_CASE(should_constexpr_multiply_checked_values)
+{
+    constexpr Checked<int> a { 3 };
+    constexpr Checked<int> b { 5 };
+    constexpr Checked<int> expected { 15 };
+    static_assert(expected == (a * b).value());
+}
+
+TEST_CASE(should_constexpr_divide_checked_values)
+{
+    constexpr Checked<int> a { 10 };
+    constexpr Checked<int> b { 2 };
+    constexpr Checked<int> expected { 5 };
+    static_assert(expected == (a / b).value());
+}
+
+TEST_CASE(should_constexpr_compare_checked_values_lhs)
+{
+    constexpr Checked<int> a { 10 };
+
+    static_assert(a > 5);
+    static_assert(a >= 10);
+    static_assert(a >= 5);
+
+    static_assert(a < 20);
+    static_assert(a <= 30);
+    static_assert(a <= 20);
+
+    static_assert(a == 10);
+    static_assert(a != 20);
+}
+
+TEST_CASE(should_constexpr_compare_checked_values_rhs)
+{
+    constexpr Checked<int> a { 10 };
+
+    static_assert(5 < a);
+    static_assert(10 <= a);
+    static_assert(5 <= a);
+
+    static_assert(20 > a);
+    static_assert(30 >= a);
+    static_assert(30 >= a);
+
+    static_assert(10 == a);
+    static_assert(20 != a);
+}
+
+TEST_CASE(should_constexpr_make_via_factory)
+{
+    [[maybe_unused]] constexpr auto value = make_checked(42);
+}
+
 TEST_MAIN(Checked)