util/StringView: add method Split()

src/util/StringView.hxx

 /*
- * Copyright (C) 2013-2017 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright 2013-2019 Max Kellermann <max.kellermann@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -33,6 +33,8 @@
 #include "ConstBuffer.hxx"
 #include "StringAPI.hxx"
 
+#include <utility>
+
 template<typename T>
 struct BasicStringView : ConstBuffer<T> {
 	typedef typename ConstBuffer<T>::size_type size_type;
@@ -65,6 +67,8 @@ struct BasicStringView : ConstBuffer<T> {
 		:ConstBuffer<T>(n) {}
 
 	using ConstBuffer<T>::empty;
+	using ConstBuffer<T>::begin;
+	using ConstBuffer<T>::end;
 	using ConstBuffer<T>::front;
 	using ConstBuffer<T>::back;
 	using ConstBuffer<T>::pop_front;
@@ -76,6 +80,20 @@ struct BasicStringView : ConstBuffer<T> {
 		return StringFind(data, ch, this->size);
 	}
 
+	/**
+	 * Split the string at the first occurrence of the given
+	 * character.  If the character is not found, then the first
+	 * value is the whole string and the second value is nullptr.
+	 */
+	gcc_pure
+	std::pair<BasicStringView<T>, BasicStringView<T>> Split(value_type ch) const noexcept {
+		const auto separator = Find(ch);
+		if (separator == nullptr)
+			return {*this, nullptr};
+
+		return {{begin(), separator}, {separator + 1, end()}};
+	}
+
 	gcc_pure
 	bool StartsWith(BasicStringView<T> needle) const noexcept {
 		return this->size >= needle.size &&