Remove use of std::reference_wrapper where possible.

What's left is *a lot* of places taking monstrous
std::vector<std::reference_wrapper> and that can't be changed to
std::vector<Containers::Reference> in a source-compatible way. Even that
would be only a temporary change, since the goal is to fully avoid
dependency on STL in those cases.

The final version of these APIs should take
Containers::ArrayView<Containers::Reference> and be implicitly
convertible froom e.g. std::vector<Containers::Reference>. That's
definitely possible, but not in time for 2019.01, so instead of forcing
users to temporary pass a `{vec.begin(), vec.size()}` everywhere instead
of just `vec`, I'm rather keeping these APIs intact.

doc/changelog.dox

@@ -61,7 +61,7 @@ See also:
 -   @ref Animation::Player::resume() that acts the same as
     @ref Animation::Player::play() "play()" except it doesn't restart the
     animation from the start if it is already playing
--   Added @ref Animation::Player::advance(T, std::initializer_list<std::reference_wrapper<Player<T, K>>>)
+-   Added @ref Animation::Player::advance(T, std::initializer_list<Containers::Reference<Player<T, K>>>)
     for advancing multiple players at the same time
 
 @subsubsection changelog-latest-new-math Math library
@@ -211,6 +211,13 @@ See also:
     @ref GL::Mesh instead of @ref std::pair of a mesh and a buffer, as the
     buffer is now owned by the mesh. This change was not possible to be done in
     a backwards-compatible way.
+-   @ref Animation::Player, @ref Audio::Listener, @ref GL::AbstractShaderProgram,
+    @ref GL::MeshView and @ref GL::Shader APIs that take a
+    @ref std::initializer_list of references were changed to use
+    @ref Corrade::Containers::Reference instead of a @ref std::reference_wrapper.
+    This change should be fully transparent to the user as the type conversion
+    is done implicitly in both cases, but you may need to add an
+    @cpp #include <Corrade/Containers/Reference.h> @ce where appropriate.
 -   Removed deprecated implicit conversion @ref Corrade::Containers::Optional
     to @cpp std::optional @ce, deprecated in January 2018. The class now
     contains an *explicit* and opt-in STL compatibility, see its documentation

doc/opengl-mapping.dox

@@ -291,7 +291,7 @@ OpenGL function                         | Matching API
 @fn_gl{MapBuffer}, \n `glMapNamedBuffer()`, \n @fn_gl_extension{MapNamedBuffer,EXT,direct_state_access}, \n @fn_gl{MapBufferRange}, \n `glMapNamedBufferRange()`, \n @fn_gl_extension{MapNamedBufferRange,EXT,direct_state_access}, \n @fn_gl{UnmapBuffer}, \n `glUnmapNamedBuffer()`, \n @fn_gl_extension{UnmapNamedBuffer,EXT,direct_state_access} | @ref GL::Buffer::map(), @ref GL::Buffer::unmap()
 @fn_gl{MemoryBarrier}, \n `glMemoryBarrierByRegion()` | @ref GL::Renderer::setMemoryBarrier(), \n @ref GL::Renderer::setMemoryBarrierByRegion()
 @fn_gl{MinSampleShading}                | @ref GL::Renderer::setMinSampleShading()
-@fn_gl{MultiDrawArrays}, \n @fn_gl{MultiDrawElements}, \n @fn_gl{MultiDrawElementsBaseVertex} | @ref GL::MeshView::draw(AbstractShaderProgram&, std::initializer_list<std::reference_wrapper<MeshView>>)
+@fn_gl{MultiDrawArrays}, \n @fn_gl{MultiDrawElements}, \n @fn_gl{MultiDrawElementsBaseVertex} | @ref GL::MeshView::draw(AbstractShaderProgram&, std::initializer_list<Containers::Reference<MeshView>>)
 @fn_gl{MultiDrawArraysIndirectCount}, \n @fn_gl{MultiDrawElementsIndirectCount} | |
 
 @subsection opengl-mapping-functions-o O

doc/snippets/MagnumAudio-scenegraph.cpp

@@ -23,6 +23,8 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
+
 #include "Magnum/Audio/Buffer.h"
 #include "Magnum/Audio/Listener.h"
 #include "Magnum/Audio/Playable.h"

doc/snippets/MagnumGL.cpp

@@ -23,6 +23,8 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
+
 #include "Magnum/Image.h"
 #include "Magnum/PixelFormat.h"
 #include "Magnum/GL/AbstractShaderProgram.h"

src/Magnum/Animation/Player.h

@@ -263,7 +263,7 @@ template<class T, class K
          *
          * Equivalent to calling @ref advance(T) for each item in @p players.
          */
-        static void advance(T time, std::initializer_list<std::reference_wrapper<Player<T, K>>> players);
+        static void advance(T time, std::initializer_list<Containers::Reference<Player<T, K>>> players);
 
         /** @brief Constructor */
         explicit Player();

src/Magnum/Animation/Player.hpp

@@ -31,8 +31,8 @@
 
 #include "Player.h"
 
-#include <functional>
 #include <Corrade/Containers/Optional.h>
+#include <Corrade/Containers/Reference.h>
 
 namespace Magnum { namespace Animation {
 
@@ -71,7 +71,7 @@ template<class T, class K> struct Player<T, K>::Track  {
 };
 #endif
 
-template<class T, class K> void Player<T, K>::advance(const T time, const std::initializer_list<std::reference_wrapper<Player<T, K>>> players) {
+template<class T, class K> void Player<T, K>::advance(const T time, const std::initializer_list<Containers::Reference<Player<T, K>>> players) {
     for(Player<T, K>& p: players) p.advance(time);
 }
 

src/Magnum/Animation/Test/PlayerTest.cpp

@@ -23,8 +23,8 @@
     DEALINGS IN THE SOFTWARE.
 */
 
-#include <functional>
 #include <sstream>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/TestSuite/Tester.h>
 #include <Corrade/TestSuite/Compare/Numeric.h>
 

src/Magnum/Audio/Listener.cpp

@@ -26,6 +26,8 @@
 
 #include "Listener.h"
 
+#include <Corrade/Containers/Reference.h>
+
 #include "Magnum/Audio/Playable.h"
 #include "Magnum/Audio/PlayableGroup.h"
 #include "Magnum/Audio/Renderer.h"
@@ -69,7 +71,7 @@ template<UnsignedInt dimensions> void Listener<dimensions>::clean(const MatrixTy
     /** @todo velocity */
 }
 
-template<UnsignedInt dimensions> void Listener<dimensions>::update(std::initializer_list<std::reference_wrapper<PlayableGroup<dimensions>>> groups) {
+template<UnsignedInt dimensions> void Listener<dimensions>::update(std::initializer_list<Containers::Reference<PlayableGroup<dimensions>>> groups) {
     /* Check if active listener just changed to this */
     if(this != activeListener) {
         /* Ensure that clean() is called also when switching between (clean)

src/Magnum/Audio/Listener.h

@@ -119,7 +119,7 @@ template<UnsignedInt dimensions> class Listener: public SceneGraph::AbstractFeat
          * listener-related configuration for @ref Renderer (position,
          * orientation, gain).
          */
-        void update(std::initializer_list<std::reference_wrapper<PlayableGroup<dimensions>>> groups);
+        void update(std::initializer_list<Containers::Reference<PlayableGroup<dimensions>>> groups);
 
         /** @brief Listener gain */
         Float gain() const { return _gain; }

src/Magnum/Audio/Test/ListenerALTest.cpp

@@ -24,6 +24,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/TestSuite/Tester.h>
 
 #include "Magnum/Audio/Context.h"

src/Magnum/DebugTools/TextureImage.cpp

@@ -35,6 +35,7 @@
 #include "Magnum/GL/Texture.h"
 
 #if defined(MAGNUM_TARGET_GLES) && !defined(MAGNUM_TARGET_GLES2)
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/AbstractShaderProgram.h"

src/Magnum/GL/AbstractShaderProgram.cpp

@@ -26,6 +26,7 @@
 #include "AbstractShaderProgram.h"
 
 #include <Corrade/Containers/Array.h>
+#include <Corrade/Containers/Reference.h>
 
 #include "Magnum/GL/Context.h"
 #include "Magnum/GL/Extensions.h"
@@ -348,7 +349,7 @@ void AbstractShaderProgram::attachShader(Shader& shader) {
     glAttachShader(_id, shader.id());
 }
 
-void AbstractShaderProgram::attachShaders(std::initializer_list<std::reference_wrapper<Shader>> shaders) {
+void AbstractShaderProgram::attachShaders(std::initializer_list<Containers::Reference<Shader>> shaders) {
     for(Shader& s: shaders) attachShader(s);
 }
 
@@ -394,7 +395,9 @@ void AbstractShaderProgram::transformFeedbackVaryingsImplementationDanglingWorka
 #endif
 #endif
 
-bool AbstractShaderProgram::link(std::initializer_list<std::reference_wrapper<AbstractShaderProgram>> shaders) {
+bool AbstractShaderProgram::link() { return link({*this}); }
+
+bool AbstractShaderProgram::link(std::initializer_list<Containers::Reference<AbstractShaderProgram>> shaders) {
     bool allSuccess = true;
 
     /* Invoke (possibly parallel) linking on all shaders */

src/Magnum/GL/AbstractShaderProgram.h

@@ -29,7 +29,6 @@
  * @brief Class @ref Magnum::GL::AbstractShaderProgram
  */
 
-#include <functional>
 #include <string>
 #include <Corrade/Containers/ArrayView.h>
 
@@ -757,7 +756,7 @@ class MAGNUM_GL_EXPORT AbstractShaderProgram: public AbstractObject {
          *      @def_gl{LINK_STATUS} and @def_gl{INFO_LOG_LENGTH},
          *      @fn_gl_keyword{GetProgramInfoLog}
          */
-        static bool link(std::initializer_list<std::reference_wrapper<AbstractShaderProgram>> shaders);
+        static bool link(std::initializer_list<Containers::Reference<AbstractShaderProgram>> shaders);
 
         #if !defined(MAGNUM_TARGET_GLES2) && !defined(MAGNUM_TARGET_WEBGL)
         /**
@@ -810,7 +809,7 @@ class MAGNUM_GL_EXPORT AbstractShaderProgram: public AbstractObject {
          * than one shader at once. Other than that there is no other
          * (performance) difference when using this function.
          */
-        void attachShaders(std::initializer_list<std::reference_wrapper<Shader>> shaders);
+        void attachShaders(std::initializer_list<Containers::Reference<Shader>> shaders);
 
         /**
          * @brief Bind attribute to given location
@@ -930,11 +929,11 @@ class MAGNUM_GL_EXPORT AbstractShaderProgram: public AbstractObject {
          * @brief Link the shader
          *
          * Links single shader. If possible, prefer to link multiple shaders
-         * at once using @ref link(std::initializer_list<std::reference_wrapper<AbstractShaderProgram>>)
+         * at once using @ref link(std::initializer_list<Containers::Reference<AbstractShaderProgram>>)
          * for improved performance, see its documentation for more
          * information.
          */
-        bool link() { return link({*this}); }
+        bool link();
 
         /**
          * @brief Get uniform location

src/Magnum/GL/Implementation/MeshState.h

@@ -59,7 +59,7 @@ struct MeshState {
     #endif
 
     #ifdef MAGNUM_TARGET_GLES
-    void(*multiDrawImplementation)(std::initializer_list<std::reference_wrapper<MeshView>>);
+    void(*multiDrawImplementation)(std::initializer_list<Containers::Reference<MeshView>>);
     #endif
 
     void(*bindVAOImplementation)(GLuint);

src/Magnum/GL/Mesh.h

@@ -926,7 +926,7 @@ class MAGNUM_GL_EXPORT Mesh: public AbstractObject {
          * @see @ref setCount(), @ref setInstanceCount(),
          *      @ref draw(AbstractShaderProgram&, TransformFeedback&, UnsignedInt),
          *      @ref MeshView::draw(AbstractShaderProgram&),
-         *      @ref MeshView::draw(AbstractShaderProgram&, std::initializer_list<std::reference_wrapper<MeshView>>),
+         *      @ref MeshView::draw(AbstractShaderProgram&, std::initializer_list<Containers::Reference<MeshView>>),
          *      @fn_gl_keyword{UseProgram}, @fn_gl_keyword{EnableVertexAttribArray},
          *      @fn_gl{BindBuffer}, @fn_gl_keyword{VertexAttribPointer},
          *      @fn_gl_keyword{DisableVertexAttribArray} or @fn_gl_keyword{BindVertexArray},

src/Magnum/GL/MeshView.cpp

@@ -36,7 +36,7 @@
 
 namespace Magnum { namespace GL {
 
-void MeshView::draw(AbstractShaderProgram& shader, std::initializer_list<std::reference_wrapper<MeshView>> meshes) {
+void MeshView::draw(AbstractShaderProgram& shader, std::initializer_list<Containers::Reference<MeshView>> meshes) {
     /* Why std::initializer_list doesn't have empty()? */
     if(!meshes.size()) return;
 
@@ -56,7 +56,7 @@ void MeshView::draw(AbstractShaderProgram& shader, std::initializer_list<std::re
 }
 
 #ifndef MAGNUM_TARGET_WEBGL
-void MeshView::multiDrawImplementationDefault(std::initializer_list<std::reference_wrapper<MeshView>> meshes) {
+void MeshView::multiDrawImplementationDefault(std::initializer_list<Containers::Reference<MeshView>> meshes) {
     CORRADE_INTERNAL_ASSERT(meshes.size());
 
     const Implementation::MeshState& state = *Context::current().state().mesh;
@@ -123,7 +123,7 @@ void MeshView::multiDrawImplementationDefault(std::initializer_list<std::referen
 #endif
 
 #ifdef MAGNUM_TARGET_GLES
-void MeshView::multiDrawImplementationFallback(std::initializer_list<std::reference_wrapper<MeshView>> meshes) {
+void MeshView::multiDrawImplementationFallback(std::initializer_list<Containers::Reference<MeshView>> meshes) {
     for(MeshView& mesh: meshes) {
         /* Nothing to draw in this mesh */
         if(!mesh._count) continue;

src/Magnum/GL/MeshView.h

@@ -29,9 +29,10 @@
  * @brief Class @ref Magnum::GL::MeshView
  */
 
-#include <functional>
 #include <initializer_list>
+#include <Corrade/Containers/Reference.h>
 
+#include "Magnum/Magnum.h"
 #include "Magnum/GL/GL.h"
 #include "Magnum/GL/OpenGL.h"
 #include "Magnum/GL/visibility.h"
@@ -88,10 +89,10 @@ class MAGNUM_GL_EXPORT MeshView {
          * @requires_gl Specifying base vertex for indexed meshes is not
          *      available in OpenGL ES or WebGL.
          */
-        static void draw(AbstractShaderProgram& shader, std::initializer_list<std::reference_wrapper<MeshView>> meshes);
+        static void draw(AbstractShaderProgram& shader, std::initializer_list<Containers::Reference<MeshView>> meshes);
 
         /** @overload */
-        static void draw(AbstractShaderProgram&& shader, std::initializer_list<std::reference_wrapper<MeshView>> meshes) {
+        static void draw(AbstractShaderProgram&& shader, std::initializer_list<Containers::Reference<MeshView>> meshes) {
             draw(shader, meshes);
         }
 
@@ -238,7 +239,7 @@ class MAGNUM_GL_EXPORT MeshView {
          * @return Reference to self (for method chaining)
          *
          * See @ref Mesh::draw(AbstractShaderProgram&) for more information.
-         * @see @ref draw(AbstractShaderProgram&, std::initializer_list<std::reference_wrapper<MeshView>>),
+         * @see @ref draw(AbstractShaderProgram&, std::initializer_list<Containers::Reference<MeshView>>),
          *      @ref draw(AbstractShaderProgram&, TransformFeedback&, UnsignedInt)
          * @requires_gl32 Extension @gl_extension{ARB,draw_elements_base_vertex}
          *      if the mesh is indexed and @ref baseVertex() is not `0`.
@@ -286,11 +287,11 @@ class MAGNUM_GL_EXPORT MeshView {
 
     private:
         #ifndef MAGNUM_TARGET_WEBGL
-        static MAGNUM_GL_LOCAL void multiDrawImplementationDefault(std::initializer_list<std::reference_wrapper<MeshView>> meshes);
+        static MAGNUM_GL_LOCAL void multiDrawImplementationDefault(std::initializer_list<Containers::Reference<MeshView>> meshes);
         #endif
-        static MAGNUM_GL_LOCAL void multiDrawImplementationFallback(std::initializer_list<std::reference_wrapper<MeshView>> meshes);
+        static MAGNUM_GL_LOCAL void multiDrawImplementationFallback(std::initializer_list<Containers::Reference<MeshView>> meshes);
 
-        std::reference_wrapper<Mesh> _original;
+        Containers::Reference<Mesh> _original;
 
         bool _countSet{};
         Int _count{}, _baseVertex{}, _instanceCount{1};

src/Magnum/GL/Shader.cpp

@@ -26,6 +26,7 @@
 #include "Shader.h"
 
 #include <Corrade/Containers/Array.h>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Assert.h>
 #include <Corrade/Utility/Debug.h>
 #include <Corrade/Utility/Directory.h>
@@ -746,7 +747,9 @@ Shader& Shader::addFile(const std::string& filename) {
     return *this;
 }
 
-bool Shader::compile(std::initializer_list<std::reference_wrapper<Shader>> shaders) {
+bool Shader::compile() { return compile({*this}); }
+
+bool Shader::compile(std::initializer_list<Containers::Reference<Shader>> shaders) {
     bool allSuccess = true;
 
     /* Allocate large enough array for source pointers and sizes (to avoid

src/Magnum/GL/Shader.h

@@ -29,7 +29,6 @@
  * @brief Class @ref Magnum::GL::Shader
  */
 
-#include <functional>
 #include <string>
 #include <vector>
 #include <Corrade/Containers/ArrayView.h>
@@ -498,7 +497,7 @@ class MAGNUM_GL_EXPORT Shader: public AbstractObject {
          *      @fn_gl_keyword{GetShader} with @def_gl{COMPILE_STATUS} and
          *      @def_gl{INFO_LOG_LENGTH}, @fn_gl_keyword{GetShaderInfoLog}
          */
-        static bool compile(std::initializer_list<std::reference_wrapper<Shader>> shaders);
+        static bool compile(std::initializer_list<Containers::Reference<Shader>> shaders);
 
         /**
          * @brief Constructor
@@ -610,11 +609,11 @@ class MAGNUM_GL_EXPORT Shader: public AbstractObject {
          * @brief Compile shader
          *
          * Compiles single shader. Prefer to compile multiple shaders at once
-         * using @ref compile(std::initializer_list<std::reference_wrapper<Shader>>)
+         * using @ref compile(std::initializer_list<Containers::Reference<Shader>>)
          * for improved performance, see its documentation for more
          * information.
          */
-        bool compile() { return compile({*this}); }
+        bool compile();
 
     private:
         Shader& setLabelInternal(Containers::ArrayView<const char> label);

src/Magnum/GL/Test/AbstractShaderProgramGLTest.cpp

@@ -24,6 +24,7 @@
 */
 
 #include <sstream>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 #include <Corrade/TestSuite/Compare/Container.h>
 

src/Magnum/GL/Test/PrimitiveQueryGLTest.cpp

@@ -23,6 +23,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Assert.h>
 #include <Corrade/Utility/Resource.h>
 

src/Magnum/GL/Test/SampleQueryGLTest.cpp

@@ -23,6 +23,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Assert.h>
 #include <Corrade/Utility/Resource.h>
 

src/Magnum/GL/Test/TransformFeedbackGLTest.cpp

@@ -23,6 +23,8 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <Corrade/Containers/Reference.h>
+
 #include "Magnum/Image.h"
 #include "Magnum/GL/AbstractShaderProgram.h"
 #include "Magnum/GL/Buffer.h"

src/Magnum/Shaders/DistanceFieldVector.cpp

@@ -25,6 +25,7 @@
 
 #include "DistanceFieldVector.h"
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/Context.h"

src/Magnum/Shaders/Flat.cpp

@@ -26,6 +26,7 @@
 #include "Flat.h"
 
 #include <Corrade/Containers/EnumSet.hpp>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/Context.h"

src/Magnum/Shaders/MeshVisualizer.cpp

@@ -27,6 +27,7 @@
 
 #include <Corrade/Containers/EnumSet.hpp>
 #include <Corrade/Containers/Optional.h>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/Context.h"

src/Magnum/Shaders/Phong.cpp

@@ -29,6 +29,7 @@
 #include <Corrade/Containers/Array.h>
 #endif
 #include <Corrade/Containers/EnumSet.hpp>
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Format.h>
 #include <Corrade/Utility/Resource.h>
 

src/Magnum/Shaders/Vector.cpp

@@ -25,6 +25,7 @@
 
 #include "Vector.h"
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/Context.h"

src/Magnum/Shaders/VertexColor.cpp

@@ -25,6 +25,7 @@
 
 #include "VertexColor.h"
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Resource.h>
 
 #include "Magnum/GL/Context.h"

src/Magnum/TextureTools/DistanceField.cpp

@@ -25,6 +25,7 @@
 
 #include "DistanceField.h"
 
+#include <Corrade/Containers/Reference.h>
 #include <Corrade/Utility/Format.h>
 #include <Corrade/Utility/Resource.h>