Range-based algorithms

本文标题的含义是"C++ algorithm是基于range的"，它是C++ algorithm的使用模式，本文对此进行总结。

下面是对本节标题的观点的说明。

Before C++20

Before C++20，algorithm基本上都是如下模式:

template <typename IntputIterator, typename OutputIterator>
OutputIterator algorithm(IntputIterator begin, IntputIterator end, OutputIterator out)
{

}

需要注意的是: C++ range-based algorithm是左闭右开的。

1、fluentcpp Smart Output Iterators: A Symmetrical Approach to Range Adaptors

Some of the algorithms of the STL have a structure in common: they take one or more ranges in input, do something more or less elaborate with them, and produce an output in a destination range.

For example, std::copy merely copies the inputs to the outputs, std::transform applies a function onto the inputs and sends the results as outputs, and std::set_difference takes two input ranges and outputs to a destination range the elements that are in the first one but not in the second.

There are several ways to express this kind of input-operation-output structure on ranges in C++. To illustrate them, let’s take the example of std::transform since it is such a central algorithm in the STL.

To make the code examples lighter, let’s suppose that we have some modified versions of STL algorithms that take an input range instead of two iterators, for instance:

2、C++ algorithms library

C++ algorithms library中的大部分algorithm是典型的“range-based algorithm”，即它们的入参一般都是：

a、InputIt first

b、InputIt last

Since C++20

C++20引入了range library，这重构了C++ algorithm，参见 C++20-Range-library 章节。