Fix emplace for types with a deleted move constructor (in the not trivially destructible case)

doc/html/variant2.html

@@ -1346,7 +1346,7 @@ and <code>U</code> occurs exactly once in <code>T&#8230;&#8203;</code>.</p>
 <dl>
 <dt class="hdlist1">Requires: </dt>
 <dd>
-<p><code>I &lt; sizeof(T&#8230;&#8203;)</code>.</p>
+<p><code>I &lt; sizeof&#8230;&#8203;(T)</code>.</p>
 </dd>
 <dt class="hdlist1">Effects:  </dt>
 <dd>
@@ -1361,6 +1361,30 @@ value as if using the expression <code>Ti(std::forward&lt;A&gt;(a)&#8230;&#8203;
 <dd>
 <p>A reference to the new contained value.</p>
 </dd>
+<dt class="hdlist1">Throws:   </dt>
+<dd>
+<p>Nothing unless the initialization of the new contained value throws.</p>
+</dd>
+<dt class="hdlist1">Exception Safety: </dt>
+<dd>
+<p>On exception:</p>
+<div class="ulist">
+<ul>
+<li>
+<p>If the list of alternatives contains <code>monostate</code>, the contained value
+is either unchanged, or <code>monostate{}</code>;</p>
+</li>
+<li>
+<p>Otherwise, if the list of alternatives contains types for which
+<code>is_nothrow_default_constructible_v</code> is <code>true</code>, the contained value
+is either unchanged, or <code>Tj{}</code>, where <code>Tj</code> is the first such alternative;</p>
+</li>
+<li>
+<p>Otherwise, the contained value is unchanged.</p>
+</li>
+</ul>
+</div>
+</dd>
 <dt class="hdlist1">Remarks:  </dt>
 <dd>
 <p>This function shall not participate in overload resolution unless
@@ -1386,7 +1410,7 @@ value as if using the expression <code>Ti(std::forward&lt;A&gt;(a)&#8230;&#8203;
 <dl>
 <dt class="hdlist1">Requires: </dt>
 <dd>
-<p><code>I &lt; sizeof(T&#8230;&#8203;)</code>.</p>
+<p><code>I &lt; sizeof&#8230;&#8203;(T)</code>.</p>
 </dd>
 <dt class="hdlist1">Effects:  </dt>
 <dd>
@@ -1401,6 +1425,30 @@ value as if using the expression <code>Ti(il, std::forward&lt;A&gt;(a)&#8230;&#8
 <dd>
 <p>A reference to the new contained value.</p>
 </dd>
+<dt class="hdlist1">Throws:   </dt>
+<dd>
+<p>Nothing unless the initialization of the new contained value throws.</p>
+</dd>
+<dt class="hdlist1">Exception Safety: </dt>
+<dd>
+<p>On exception:</p>
+<div class="ulist">
+<ul>
+<li>
+<p>If the list of alternatives contains <code>monostate</code>, the contained value
+is either unchanged, or <code>monostate{}</code>;</p>
+</li>
+<li>
+<p>Otherwise, if the list of alternatives contains types for which
+<code>is_nothrow_default_constructible_v</code> is <code>true</code>, the contained value
+is either unchanged, or <code>Tj{}</code>, where <code>Tj</code> is the first such alternative;</p>
+</li>
+<li>
+<p>Otherwise, the contained value is unchanged.</p>
+</li>
+</ul>
+</div>
+</dd>
 <dt class="hdlist1">Remarks:  </dt>
 <dd>
 <p>This function shall not participate in overload resolution unless
@@ -2141,7 +2189,7 @@ the <a href="http://www.boost.org/LICENSE_1_0.txt">Boost Software License, Versi
 </div>
 <div id="footer">
 <div id="footer-text">
-Last updated 2019-02-22 19:16:54 GTBST
+Last updated 2019-02-22 19:21:28 GTBST
 </div>
 </div>
 <style>

doc/variant2/reference.adoc

@@ -502,6 +502,15 @@ Effects:  ::
   value as if using the expression `Ti(std::forward<A>(a)...)`.
 Ensures:  :: `index() == I`.
 Returns:  :: A reference to the new contained value.
+Throws:   ::
+  Nothing unless the initialization of the new contained value throws.
+Exception Safety: :: On exception:
+  - If the list of alternatives contains `monostate`, the contained value
+    is either unchanged, or `monostate{}`;
+  - Otherwise, if the list of alternatives contains types for which
+    `is_nothrow_default_constructible_v` is `true`, the contained value
+    is either unchanged, or `Tj{}`, where `Tj` is the first such alternative;
+  - Otherwise, the contained value is unchanged.
 Remarks:  ::
   This function shall not participate in overload resolution unless
   `std::is_constructible_v<Ti, A...>` is `true`.
@@ -520,6 +529,15 @@ Effects:  ::
   value as if using the expression `Ti(il, std::forward<A>(a)...)`.
 Ensures:  :: `index() == I`.
 Returns:  :: A reference to the new contained value.
+Throws:   ::
+  Nothing unless the initialization of the new contained value throws.
+Exception Safety: :: On exception:
+  - If the list of alternatives contains `monostate`, the contained value
+    is either unchanged, or `monostate{}`;
+  - Otherwise, if the list of alternatives contains types for which
+    `is_nothrow_default_constructible_v` is `true`, the contained value
+    is either unchanged, or `Tj{}`, where `Tj` is the first such alternative;
+  - Otherwise, the contained value is unchanged.
 Remarks:  ::
   This function shall not participate in overload resolution unless
   `std::is_constructible_v<Ti, std::initializer_list<V>&, A...>` is `true`.

include/boost/variant2/variant.hpp

@@ -651,12 +651,16 @@ template<class... T> struct variant_base_impl<true, true, T...>
 
     template<std::size_t J, class U, bool B, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_true, mp11::mp_bool<B>, A&&... a )
     {
+        static_assert( std::is_nothrow_constructible<U, A&&...>::value, "Logic error: U must be nothrow constructible from A&&..." );
+
         st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
         ix_ = J;
     }
 
     template<std::size_t J, class U, class... A> BOOST_CXX14_CONSTEXPR void emplace_impl( mp11::mp_false, mp11::mp_true, A&&... a )
     {
+        static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );
+
         U tmp( std::forward<A>(a)... );
 
         st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
@@ -665,34 +669,24 @@ template<class... T> struct variant_base_impl<true, true, T...>
 
     template<std::size_t J, class U, class... A> void emplace_impl( mp11::mp_false, mp11::mp_false, A&&... a )
     {
-        if( can_be_valueless<T...>::value )
+        static_assert( can_be_valueless<T...>::value, "Logic error: T... must have a fallback type" );
+
+        std::size_t const K = valueless_index<T...>::value;
+
+        static_assert( K < sizeof...(T), "Logic error: T... must have a fallback index" );
+
+        try
         {
-            std::size_t const K = valueless_index<T...>::value;
-
-            assert( K < sizeof...(T) );
-
-            try
-            {
-                st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
-                ix_ = J;
-            }
-            catch( ... )
-            {
-                st1_.emplace( mp11::mp_size_t<K+1>() );
-                ix_ = K+1;
-
-                throw;
-            }
-        }
-        else
-        {
-            assert( std::is_nothrow_move_constructible<U>::value );
-
-            U tmp( std::forward<A>(a)... );
-
-            st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
+            st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
             ix_ = J;
         }
+        catch( ... )
+        {
+            st1_.emplace( mp11::mp_size_t<K+1>() );
+            ix_ = K+1;
+
+            throw;
+        }
     }
 
     template<std::size_t I, class... A> BOOST_CXX14_CONSTEXPR void emplace( A&&... a )
@@ -700,7 +694,10 @@ template<class... T> struct variant_base_impl<true, true, T...>
         std::size_t const J = I+1;
         using U = mp11::mp_at_c<variant<T...>, I>;
 
-        this->emplace_impl<J, U>( std::is_nothrow_constructible<U, A&&...>(), mp11::mp_all<detail::is_trivially_move_constructible<U>, detail::is_trivially_move_assignable<T>...>(), std::forward<A>(a)... );
+        constexpr bool B1 = can_be_valueless<T...>::value;
+        constexpr bool B2 = mp11::mp_all<detail::is_trivially_move_constructible<U>, detail::is_trivially_move_assignable<T>...>::value;
+
+        this->emplace_impl<J, U>( std::is_nothrow_constructible<U, A&&...>(), mp11::mp_bool<B2 || !B1>(), std::forward<A>(a)... );
     }
 };
 
@@ -839,51 +836,61 @@ template<class... T> struct variant_base_impl<false, true, T...>
         return st1_.get( mp11::mp_size_t<I+1>() );
     }
 
+    template<std::size_t J, class U, class... A> void emplace_impl( mp11::mp_int<0>, A&&... a )
+    {
+        static_assert( std::is_nothrow_constructible<U, A&&...>::value, "Logic error: U must be nothrow constructible from A&&..." );
+
+        _destroy();
+
+        st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
+        ix_ = J;
+    }
+
+    template<std::size_t J, class U, class... A> void emplace_impl( mp11::mp_int<1>, A&&... a )
+    {
+        static_assert( can_be_valueless<T...>::value, "Logic error: T... must have a fallback type" );
+
+        std::size_t const K = valueless_index<T...>::value;
+
+        static_assert( K < sizeof...(T), "Logic error: T... must have a fallback index" );
+
+        _destroy();
+
+        try
+        {
+            st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
+            ix_ = J;
+        }
+        catch( ... )
+        {
+            st1_.emplace( mp11::mp_size_t<K+1>() );
+            ix_ = K+1;
+
+            throw;
+        }
+    }
+
+    template<std::size_t J, class U, class... A> void emplace_impl( mp11::mp_int<2>, A&&... a )
+    {
+        static_assert( std::is_nothrow_move_constructible<U>::value, "Logic error: U must be nothrow move constructible" );
+
+        U tmp( std::forward<A>(a)... );
+
+        _destroy();
+
+        st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
+        ix_ = J;
+    }
+
     template<std::size_t I, class... A> void emplace( A&&... a )
     {
         size_t const J = I+1;
 
         using U = mp11::mp_at_c<variant<T...>, I>;
 
-        if( std::is_nothrow_constructible<U, A...>::value )
-        {
-            _destroy();
+        int const D = std::is_nothrow_constructible<U, A&&...>::value? 0: ( can_be_valueless<T...>::value? 1: 2 );
 
-            st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
-            ix_ = J;
-        }
-        else if( can_be_valueless<T...>::value )
-        {
-            std::size_t const K = valueless_index<T...>::value;
-
-            assert( K < sizeof...(T) );
-
-            _destroy();
-
-            try
-            {
-                st1_.emplace( mp11::mp_size_t<J>(), std::forward<A>(a)... );
-                ix_ = J;
-            }
-            catch( ... )
-            {
-                st1_.emplace( mp11::mp_size_t<K+1>() );
-                ix_ = K+1;
-
-                throw;
-            }
-        }
-        else
-        {
-            assert( std::is_nothrow_move_constructible<U>::value );
-
-            U tmp( std::forward<A>(a)... );
-
-            _destroy();
-
-            st1_.emplace( mp11::mp_size_t<J>(), std::move(tmp) );
-            ix_ = J;
-        }
+        this->emplace_impl<J, U>( mp11::mp_int<D>(), std::forward<A>(a)... );
     }
 };
 

test/variant_emplace_type.cpp

@@ -57,6 +57,21 @@ STATIC_ASSERT( !std::is_nothrow_move_constructible<X2>::value );
 STATIC_ASSERT( !std::is_nothrow_copy_assignable<X2>::value );
 STATIC_ASSERT( !std::is_nothrow_move_assignable<X2>::value );
 
+struct Y1
+{
+};
+
+struct Y2
+{
+    ~Y2() {}
+};
+
+struct Guard
+{
+    explicit Guard(int) {}
+    Guard(Guard&&) = delete;
+};
+
 int main()
 {
     {
@@ -165,5 +180,15 @@ int main()
         BOOST_TEST_EQ( get<0>(v).v, 4 );
     }
 
+    {
+        variant<Y1, Guard> v;
+        v.emplace<Guard>( 1 );
+    }
+
+    {
+        variant<Y2, Guard> v;
+        v.emplace<Guard>( 1 );
+    }
+
     return boost::report_errors();
 }