{

typedef std::string base;

friend string_builder make_string_builder();

private: // CONSTRUCTORS

/// Initializes an empty instance of the string_builder class.

///

/// This constructor is private. Use make_string_builder(...)

/// function with matching signature instead.

string_builder_impl() = default;

public: // METHODS

/// A string representing the current type.

virtual string to_string() override

{

// Returns a copy of the string, not a reference to the same string

// Further changes to string_builder will not affect the previously

// returned string.

return make_string(*this);

}

/// Appends the string returned by processing a composite format string, which contains

/// zero or more format items, to this instance. Each format item is replaced by the

/// string representation of a corresponding object argument.

template <typename First, typename ...Args>

void append_format(const string& format, const First& f, const Args& ...args)

{

*this += *string::format(format, f, args...);

}

/// Appends the string representation of a specified object to this instance.

template <typename T>

void append(const T& arg)

{

*this += *string::format("{0}", arg);

}

/// Appends a copy of a specified string and the default

/// line terminator, to the end of this instance.

template <typename ...Args>

void append_line(const Args& ...args)

{

append(args...);

append_line();

}

/// Appends the default line terminator, to the end of this instance.

void append_line()

{

*this += *environment::make_line;

}

/// Removes all characters from the current string_builder instance.

void clear()

{

this->clear();

}