Cross Platform Widgets Toolkit -- Naive Approach

crossplatform_widgets.cpp

namespace ToolkitCode {
	class IButton {
		virtual void setTitle(const string &title) = 0;
		virtual void doOnClick(std::function<void()> handler) = 0;
	};

	class Win32APIButton : public IButton {
		virtual void setTitle(const string &title) = 0;
		virtual void doOnClick(std::function<void()> handler) = 0;
	};

	class WinFormsButton : public IButton  {
		virtual void setTitle(const string &title) = 0;
		virtual void doOnClick(std::function<void()> handler) = 0;
	};

	class GTKButton : public IButton  {
		virtual void setTitle(const string &title) override;
		virtual void doOnClick(std::function<void()> handler) override;
	};

	class QtButton : public IButton  {
		virtual void setTitle(const string &title) = 0;
		virtual void doOnClick(std::function<void()> handler) override;
	};
}

namespace ClientCode {
	enum class UIFlavor {
		GTK,
		WinForms,
		Win32,
		QT
	};

	class ProgramOptions {
		uiFlavor: UIFlavor;
	};

	void createUI() {
		IButton *createDocumentButton,
				*saveDocumentButton,
				*loadDocumentButton;

		ProgramOptions options = getActualOptions();

		if (options.uiFlavor == GTK) {
			createDocumentButton = new GTKButton();
			saveDocumentButton = new GTKButton();
			loadDocumentButton = new GTKButton();
		} else if (options.uiFlavor == WinForms) {
			createDocumentButton = new WinFormsButton();
			saveDocumentButton = new WinFormsButton();
			loadDocumentButton = new WinFormsButton();
		} else if (options.uiFlavor == Win32) {
			createDocumentButton = new Win32APIButton();
			saveDocumentButton = new Win32APIButton();
			loadDocumentButton = new Win32APIButton();
		} else if (options.uiFlavor == Qt) {
			createDocumentButton = new QtButton();
			saveDocumentButton = new QtButton();
			loadDocumentButton = new QtButton();
		}
	}
};