Add std::optional

changelog/std_optional.dd

@@ -0,0 +1,3 @@
+Added `core.stdcpp.optional`.
+
+Added `core.stdcpp.optional`, which links against C++ `std::optional`

mak/COPY

@@ -86,6 +86,7 @@ COPY=\
 	$(IMPDIR)\core\stdcpp\exception.d \
 	$(IMPDIR)\core\stdcpp\memory.d \
 	$(IMPDIR)\core\stdcpp\new_.d \
+	$(IMPDIR)\core\stdcpp\optional.d \
 	$(IMPDIR)\core\stdcpp\string.d \
 	$(IMPDIR)\core\stdcpp\string_view.d \
 	$(IMPDIR)\core\stdcpp\type_traits.d \

mak/DOCS

@@ -47,6 +47,7 @@ DOCS=\
 	$(DOCDIR)\core_stdcpp_array.html \
 	$(DOCDIR)\core_stdcpp_exception.html \
 	$(DOCDIR)\core_stdcpp_new_.html \
+	$(DOCDIR)\core_stdcpp_optional.html \
 	$(DOCDIR)\core_stdcpp_string.html \
 	$(DOCDIR)\core_stdcpp_string_view.html \
 	$(DOCDIR)\core_stdcpp_typeinfo.html \

mak/SRCS

@@ -86,6 +86,7 @@ SRCS=\
 	src\core\stdcpp\exception.d \
 	src\core\stdcpp\memory.d \
 	src\core\stdcpp\new_.d \
+	src\core\stdcpp\optional.d \
 	src\core\stdcpp\string.d \
 	src\core\stdcpp\string_view.d \
 	src\core\stdcpp\type_traits.d \

src/core/stdcpp/optional.d

@@ -0,0 +1,201 @@
+/**
+ * D header file for interaction with C++ std::optional.
+ *
+ * Copyright: Copyright (c) 2018 D Language Foundation
+ * License: Distributed under the
+ *      $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
+ *    (See accompanying file LICENSE)
+ * Authors:   Manu Evans
+ * Source:    $(DRUNTIMESRC core/stdcpp/optional.d)
+ */
+
+module core.stdcpp.optional;
+
+import core.stdcpp.exception : exception;
+
+version (CppRuntime_DigitalMars)
+{
+    pragma(msg, "std::optional not supported by DMC");
+}
+version (CppRuntime_Clang)
+{
+    private alias AliasSeq(Args...) = Args;
+    private enum StdNamespace = AliasSeq!("std", "__1");
+}
+else
+{
+    private enum StdNamespace = "std";
+}
+
+
+extern(C++, "std")
+{
+    ///
+    class bad_optional_access : exception
+    {
+    @nogc:
+        ///
+        this(const(char)* message = "bad exception") nothrow { super(message); }
+    }
+}
+
+
+extern(C++, (StdNamespace)):
+
+///
+struct nullopt_t {}
+
+///
+enum nullopt_t nullopt = nullopt_t();
+
+///
+struct in_place_t {}
+
+///
+enum in_place_t in_place = in_place_t();
+
+/**
+ * D language counterpart to C++ std::optional.
+ *
+ * C++ reference: $(LINK2 https://en.cppreference.com/w/cpp/utility/optional)
+ */
+extern(C++, class) struct optional(T)
+{
+    static assert(!is(Unqual!T == nullopt_t), "T in optional!T cannot be nullopt_t (N4659 23.6.2 [optional.syn]/1).");
+    static assert(!is(Unqual!T == in_place_t), "T in optional!T cannot be in_place_t (N4659 23.6.2 [optional.syn]/1).");
+    static assert(!__traits(hasMember, T, "__xpostblit"), "T in optional!T may not have a postblit `this(this)` constructor. Use copy constructor instead.");
+//    static assert(is_reference_v<_Ty> || is_object_v<_Ty>, "T in optional!T must be an object type (N4659 23.6.3 [optional.optional]/3).");
+//    static assert(is_destructible_v<_Ty> && !is_array_v<_Ty>, "T in optional!T must satisfy the requirements of Destructible (N4659 23.6.3 [optional.optional]/3).");
+
+    import core.internal.traits : AliasSeq, Unqual, hasElaborateDestructor, hasElaborateCopyConstructor, hasElaborateDestructor;
+    import core.lifetime : forward, moveEmplace, core_emplace = emplace;
+
+extern(D):
+pragma(inline, true):
+
+    ///
+    this(nullopt_t) pure nothrow @nogc @safe
+    {
+    }
+
+    ///
+    this(Args...)(in_place_t, auto ref Args args)
+    {
+        static if (Args.length == 1 && is(Unqual!(Args[0]) == T))
+            moveEmplace(args[0], _value);
+        else
+            core_emplace(&_value, forward!args);
+        _engaged = true;
+    }
+
+    static if (hasElaborateCopyConstructor!T)
+    {
+        ///
+        this(ref return scope inout(optional) rhs) inout
+        {
+            _engaged = rhs._engaged;
+            if (rhs._engaged)
+                core_emplace(cast(T*)&_value, rhs._value);
+        }
+    }
+
+    static if (hasElaborateDestructor!T)
+    {
+        ///
+        ~this()
+        {
+            if (_engaged)
+                destroy!false(_value);
+        }
+    }
+
+    ///
+    void opAssign(nullopt_t)
+    {
+        reset();
+    }
+
+    ///
+    void opAssign()(auto ref optional!T rhs)
+    {
+        if (rhs._engaged)
+            opAssign(forward!rhs._value);
+        else
+            reset();
+    }
+
+    ///
+    void opAssign()(auto ref T rhs)
+    {
+        if (_engaged)
+            _value = forward!rhs;
+        else
+        {
+            core_emplace(&_value, forward!rhs);
+            _engaged = true;
+        }
+    }
+
+    ///
+    bool opCast(T : bool)() const pure nothrow @nogc @safe
+    {
+        return has_value();
+    }
+
+    ///
+    void reset()
+    {
+        static if (hasElaborateDestructor!T)
+        {
+            if (_engaged)
+            {
+                destroy!false(_value);
+                _engaged = false;
+            }
+        }
+        else
+            _engaged = false;
+    }
+
+    ///
+    ref T emplace(Args...)(auto ref Args args)
+    {
+        reset();
+        core_emplace(&_value, forward!args);
+        _engaged = true;
+        return _value;
+    }
+
+    ///
+    bool has_value() const pure nothrow @nogc @safe
+    {
+        return _engaged;
+    }
+
+    // TODO: return by-val (move _value) if `this` is an rvalue... (auto ref return?)
+    ///
+    ref inout(T) value() inout return pure @trusted // @nogc //(DIP1008)
+        in (_engaged == true)
+    {
+        // TODO: support C++ exceptions?
+//        if (!_engaged)
+//            throw new bad_optional_access();
+        return _value;
+    }
+
+    // TODO: return by-val (move _value) if `this` is an rvalue... (auto ref return?)
+    ///
+    ref inout(T) value_or(scope return ref inout(T) or) inout return pure nothrow @nogc @trusted
+    {
+        return _engaged ? _value : or;
+    }
+
+private:
+    // amazingly, MSVC, Clang and GCC all share the same struct!
+    union
+    {
+        ubyte _dummy = 0;
+        Unqual!T _value = void;
+    }
+    bool _engaged = false;
+}