Introduced Formatter Class to libzim

Code from: openzim/zim-tools#158 Fix #432

src/tools.h

@@ -27,6 +27,7 @@
 #include <map>
 #include <vector>
 #include "config.h"
+#include <sstream>
 
 #include <zim/item.h>
 
@@ -70,6 +71,36 @@ namespace zim {
     return count;
   }
 
+  /**
+   * @brief Stringstream Class to use itself as the stream object 
+   * returned by << operator. (std::stringstream returns an std::ostream). 
+   * Allows a one-line stringstream to str conversion, e.g. use_str(Formatter()
+   * << "foo" << variable);
+   *
+   */
+  class Formatter
+  {
+  public:
+    Formatter() {}
+    ~Formatter() {}
+
+    template <typename Type> Formatter &operator<<(const Type &value)
+    {
+      stream_ << value;
+      return *this;
+    }
+
+    operator std::string() const { return stream_.str(); }
+
+  private:
+    /* Disable copy and assignment constructors */
+    Formatter(const Formatter &) = delete;
+    Formatter &operator=(Formatter &) = delete;
+
+    /* Simple composition with std::stringstream */
+    std::stringstream stream_;
+  };
+
 // Xapian based tools
 #if defined(ENABLE_XAPIAN)
   std::string removeAccents(const std::string& text);