feat: add forward declaration header

Author: nfrechette

includes/sjson/fwd.h

@@ -0,0 +1,57 @@
+#pragma once
+
+////////////////////////////////////////////////////////////////////////////////
+// The MIT License (MIT)
+//
+// Copyright (c) 2022 Nicholas Frechette, Cody Jones, and sjson-cpp contributors
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+////////////////////////////////////////////////////////////////////////////////
+
+#include "sjson/version.h"
+
+////////////////////////////////////////////////////////////////////////////////
+// This header provides forward declarations for all public sjson-cpp types.
+// Forward declaring symbols from a 3rd party library is a bad idea, use this
+// header instead.
+// See also: https://blog.libtorrent.org/2017/12/forward-declarations-and-abi/
+////////////////////////////////////////////////////////////////////////////////
+
+namespace sjson
+{
+    SJSON_CPP_IMPL_VERSION_NAMESPACE_BEGIN
+
+    // Core
+    class runtime_assert;
+    class StringView;
+
+    // Parser
+    struct ParserError;
+    struct ParserState;
+    struct Parser;
+
+    // Writer
+    class StreamWriter;
+    class FileStreamWriter;
+    class ArrayWriter;
+    class ObjectWriter;
+    class Writer;
+
+    SJSON_CPP_IMPL_VERSION_NAMESPACE_END
+}

tests/sources/test_header_fwd.cpp

@@ -0,0 +1,25 @@
+////////////////////////////////////////////////////////////////////////////////
+// The MIT License (MIT)
+//
+// Copyright (c) 2022 Nicholas Frechette, Cody Jones, and sjson-cpp contributors
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+////////////////////////////////////////////////////////////////////////////////
+
+#include <sjson/fwd.h>