Move the XML writer to its own file

src/CMakeLists.txt

@@ -29,6 +29,7 @@ set (SFIZZ_HEADERS
     sfizz/Debug.h
     sfizz/utility/NumericId.h
     sfizz/utility/SpinMutex.h
+    sfizz/utility/XmlHelpers.h
     sfizz/modulations/ModId.h
     sfizz/modulations/ModKey.h
     sfizz/modulations/ModKeyHash.h

src/sfizz/Synth.cpp

@@ -19,6 +19,7 @@
 #include "modulations/sources/Controller.h"
 #include "modulations/sources/LFO.h"
 #include "modulations/sources/FlexEnvelope.h"
+#include "utility/XmlHelpers.h"
 #include "pugixml.hpp"
 #include "absl/algorithm/container.h"
 #include "absl/memory/memory.h"
@@ -1301,25 +1302,9 @@ std::string sfz::Synth::exportMidnam(absl::string_view model) const
         }
     }
 
-    ///
+    string_xml_writer writer;
-    struct string_writer : pugi::xml_writer {
-        std::string result;
-
-        string_writer()
-        {
-            result.reserve(8192);
-        }
-
-        void write(const void* data, size_t size) override
-        {
-            result.append(static_cast<const char*>(data), size);
-        }
-    };
-
-    ///
-    string_writer writer;
     doc.save(writer);
-    return std::move(writer.result);
+    return std::move(writer.str());
 }
 
 const sfz::Region* sfz::Synth::getRegionView(int idx) const noexcept

src/sfizz/utility/XmlHelpers.h

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+#include <pugixml.hpp>
+#include <string>
+
+class string_xml_writer : public pugi::xml_writer {
+public:
+    explicit string_xml_writer(size_t capacity = 8192)
+    {
+        result_.reserve(capacity);
+    }
+
+    void write(const void* data, size_t size) override
+    {
+        result_.append(static_cast<const char*>(data), size);
+    }
+
+    std::string& str() noexcept
+    {
+        return result_;
+    }
+
+private:
+    std::string result_;
+};