string_view: implement modifiers API for string_view

- add remove_prefix, remove_suffix and swap for string_view

Author: KFilipek

include/libpmemobj++/string_view.hpp

@@ -13,6 +13,7 @@
 #include <limits>
 #include <stdexcept>
 #include <string>
+#include <utility>
 
 #if __cpp_lib_string_view
 #include <string_view>
@@ -88,6 +89,10 @@ class basic_string_view {
 	constexpr const_reference front() const noexcept;
 	constexpr const_reference back() const noexcept;
 
+	void remove_prefix(size_type n);
+	void remove_suffix(size_type n);
+	void swap(basic_string_view &v) noexcept;
+
 	int compare(const basic_string_view &other) const noexcept;
 
 private:
@@ -320,6 +325,47 @@ basic_string_view<CharT, Traits>::front() const noexcept
 	return operator[](0);
 }
 
+/**
+ * Moves the start of the view forward by n characters.
+ * The behavior is undefined if n > size().
+ *
+ * @param[in] n number of characters to remove from the start of the view
+ */
+template <typename CharT, typename Traits>
+void
+basic_string_view<CharT, Traits>::remove_prefix(size_type n)
+{
+	data_ += n;
+	size_ -= n;
+}
+
+/**
+ * Moves the end of the view back by n characters.
+ * The behavior is undefined if n > size().
+ *
+ * @param[in] n number of characters to remove from the end of the view
+ */
+template <typename CharT, typename Traits>
+void
+basic_string_view<CharT, Traits>::remove_suffix(size_type n)
+{
+	size_ -= n;
+}
+
+/**
+ * Exchanges the view with that of v.
+ *
+ * @param[in] v view to swap with
+ */
+template <typename CharT, typename Traits>
+void
+basic_string_view<CharT, Traits>::swap(
+	basic_string_view<CharT, Traits> &v) noexcept
+{
+	std::swap(data_, v.data_);
+	std::swap(size_, v.size_);
+}
+
 /**
  * Compares this string_view with other. Works in the same way as
  * std::basic_string::compare.