@@ -6,10 +6,97 @@ order: 10
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77# Chapter 10 Outlook: Introduction of C++20
88
9+ [ TOC]
910
11+ C++20 seems to be an exciting update.
12+ For example, as early as C++11, the ` Concept ` ,
13+ which was eager to call for high-altitude but ultimately lost, is now on the line.
14+ The C++ Organizing Committee decided to vote to finalize C++20 with many proposals,
15+ such as ** Concepts** /** Module** /** Coroutine** /** Ranges** / and so on.
16+ In this chapter we'll take a look at some of the important features that
17+ C++20 will introduce.
18+
19+ ## Concept
20+
21+ Concept is a further enhancement to C++ template programming.
22+ In simple terms, the concept is a compile-time feature.
23+ It allows the compiler to evaluate template parameters at compile time,
24+ greatly enhancing our experience with template programming in C++.
25+ When programming with templates, we often encounter a variety of heinous errors.
26+ This is because we have so far been unable to check and limit template parameters.
27+ For example, the following two lines of code can cause a lot of
28+ almost unreadable compilation errors:
29+
30+ ``` cpp
31+ #include < list>
32+ #include < algorithm>
33+ int main () {
34+ std::list<int> l = {1, 2, 3};
35+ std::sort (l.begin(), l.end());
36+ return 0;
37+ }
38+ ```
39+
40+ The root cause of this code error is that ` std::sort ` must provide
41+ a random iterator for the sorting container, otherwise it will not be used,
42+ and we know that ` std::list ` does not support random access.
43+ In the conceptual language, the iterator in ` std::list ` does not satisfy
44+ the constraint of the concept of random iterators in ` std::sort ` .
45+ After introducing the concept, we can constrain the template parameters
46+ like this:
47+
48+ ``` cpp
49+ template <typename T>
50+ requires Sortable<T> // Sortable is a concept
51+ void sort (T& c);
52+ ```
53+
54+ abbreviate as:
55+
56+ ```cpp
57+ template<Sortable T> // T is a Sortable typename
58+ void sort(T& c)
59+ ```
60+
61+ Even use it directly as a type:
62+
63+ ``` cpp
64+ void sort (Sortable& c); // c is a Sortable type object
65+ ```
66+
67+ Let's look at a practical example.
68+
69+ TODO
70+
71+ ## Module
72+
73+ TODO
74+
75+ ## Contract
76+
77+ TODO
78+
79+ ## Range
80+
81+ TODO
82+
83+ ## Coroutine
84+
85+ TODO
86+
87+ ## Conclusion
88+
89+ In general, I finally saw the exciting features of Concepts/Ranges/Modules in C++20.
90+ This is still full of charm for a programming language that is already in its thirties.
1091
1192[Table of Content](./toc.md) | [Previous Chapter](./09-others.md) | [Next Chapter](./appendix1.md)
1293
94+ ## Further Readings
95+
96+ - [Why Concepts didn't make C++17？](http://honermann.net/blog/2016/03/06/why-concepts-didnt-make-cxx17/)
97+ - [C++11/14/17/20 Compiler Support](http://en.cppreference.com/w/cpp/compiler_support)
98+ - [C++ History](https://en.cppreference.com/w/cpp/language/history)
99+
13100## Licenses
14101
15102<a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-nd/4.0/88x31.png" /></a><br />This work was written by [Ou Changkun](https://changkun.de) and licensed under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License</a>. The code of this repository is open sourced under the [MIT license](../../LICENSE).
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