Add defaulted<Value, defaults...> and zeroed<Value>

Author: polytypic

internals/testing/defaulted_test.cpp

@@ -0,0 +1,26 @@
+#include "dumpster_v1/defaulted.hpp"
+
+#include "testing_v1/test.hpp"
+
+using namespace testing_v1;
+
+auto defaulted_test = test([]() {
+  {
+    dumpster_v1::defaulted<int, 42> x;
+    verify(x.value == 42);
+    x = 101;
+    verify(x == 101);
+  }
+  {
+    dumpster_v1::defaulted<short, 42> x(short(101));
+    verify(x == 101);
+  }
+  {
+    const dumpster_v1::zeroed<std::size_t> x;
+    verify(x == 0);
+  }
+  {
+    dumpster_v1::zeroed<char *> x;
+    verify(x == nullptr);
+  }
+});

provides/include/dumpster_v1/defaulted.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "dumpster_v1/synopsis.hpp"
+
+#include <utility>
+
+template <class Value, auto... defaults>
+dumpster_v1::defaulted<Value, defaults...>::defaulted() : value(defaults...) {}
+
+template <class Value, auto... defaults>
+template <class... Arguments>
+dumpster_v1::defaulted<Value, defaults...>::defaulted(Arguments &&... arguments)
+    : value(std::forward<Arguments>(arguments)...) {}
+
+template <class Value, auto... defaults>
+dumpster_v1::defaulted<Value, defaults...>::operator const Value &() const {
+  return value;
+}
+
+template <class Value, auto... defaults>
+dumpster_v1::defaulted<Value, defaults...>::operator Value &() {
+  return value;
+}

provides/include/dumpster_v1/synopsis.hpp

@@ -4,6 +4,34 @@
 
 namespace dumpster_v1 {
 
+// defaulted.hpp ===============================================================
+
+// Default initializes a value with the given arguments.
+template <class Value, auto... defaults> struct defaulted {
+  /// Default constructor initializes value with the defaults given as template
+  /// arguments.
+  defaulted();
+
+  /// Non-default constructor initializes value with given arguments.
+  template <class... Arguments> defaulted(Arguments &&... arguments);
+
+  /// Implicit conversion to const reference for convenience.
+  operator const Value &() const;
+
+  /// Implicit conversion to reference for convenience.
+  operator Value &();
+
+  /// The value is directly accessible as there is no reason to hide it.
+  Value value;
+};
+
+// Zero initializes a value of the given type.
+template <class Value>
+using zeroed =
+    defaulted<Value,
+              std::conditional_t<std::is_pointer_v<Value>, std::nullptr_t, int>(
+                  0)>;
+
 // finally.hpp =================================================================
 
 /// Finalizer that invokes stored action when destroyed.