Add DEFINE_HAS_METHOD() and tests.

Author: evoskuil

include/bitcoin/system/constraints.hpp

@@ -280,6 +280,16 @@ using if_byte_insertable = bool_if<
     std::is_base_of<std_vector<uint8_t>, Type>::value ||
     std::is_base_of<std::vector<uint8_t>, Type>::value>;
 
+/// define: DEFINE_HAS_METHOD(flush)
+/// usage: bool_if<has_flush_v<Type>>
+#define DEFINE_HAS_METHOD(method) \
+template <typename T, typename = void> \
+struct has_##method : std::false_type {}; \
+template <typename T> \
+struct has_##method<T, std::void_t<decltype(&T::method)>> : std::true_type {}; \
+template <typename Type> \
+static constexpr bool has_##method##_v = has_##method<Type>::value
+
 } // namespace libbitcoin
 
 #endif

include/bitcoin/system/types.hpp

@@ -183,8 +183,9 @@ BC_PUSH_WARNING(NO_DYNAMIC_ARRAY_INDEXING)
 BC_PUSH_WARNING(NO_ARRAY_INDEXING)
 
 template <size_t Size>
-struct text_t
+class text_t
 {
+public:
     std::array<uint8_t, Size - 1> data;
     CONSTEVAL text_t(const char (&string)[Size]) noexcept
       : data(to_array(string)) {}

test/constraints.cpp

@@ -652,4 +652,21 @@ static_assert(is_defined<if_byte_insertable<std_vector<uint8_t>>>);
 ////static_assert(!is_defined<if_byte_insertable<std::array<uint8_t, 42>>>);
 ////static_assert(!is_defined<if_byte_insertable<std::u32string>>);
 ////static_assert(!is_defined<if_byte_insertable<std_vector<uint32_t>>>);
-////static_assert(!is_defined<if_byte_insertable<uint32_t>>);
+////static_assert(!is_defined<if_byte_insertable<uint32_t>>);
+
+// HAS_METHOD
+
+struct not_has { void foobar_() {} };
+struct has_args { void foobar(bool, int) {} };
+struct has_base { void foobar() {} };
+struct has_publics_derived : public has_base {};
+struct has_protect_derived : protected has_base {};
+struct has_private_derived : private has_base {};
+
+DEFINE_HAS_METHOD(foobar);
+static_assert(!has_foobar_v<not_has>);
+static_assert(has_foobar_v<has_args>);
+static_assert(has_foobar_v<has_base>);
+static_assert(has_foobar_v<has_publics_derived>);
+static_assert(!has_foobar_v<has_protect_derived>);
+static_assert(!has_foobar_v<has_private_derived>);