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102 lines
3.1 KiB
Markdown
102 lines
3.1 KiB
Markdown
---
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title: "Chapter 10 Outlook: Introduction of C++20"
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type: book-en-us
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order: 10
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---
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# Chapter 10 Outlook: Introduction of C++20
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[TOC]
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C++20 seems to be an exciting update.
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For example, as early as C++11, the `Concept`,
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which was eager to call for high-altitude but ultimately lost, is now on the line.
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The C++ Organizing Committee decided to vote to finalize C++20 with many proposals,
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such as **Concepts**/**Module**/**Coroutine**/**Ranges**/ and so on.
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In this chapter we'll take a look at some of the important features that
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C++20 will introduce.
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## Concept
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Concept is a further enhancement to C++ template programming.
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In simple terms, the concept is a compile-time feature.
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It allows the compiler to evaluate template parameters at compile time,
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greatly enhancing our experience with template programming in C++.
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When programming with templates, we often encounter a variety of heinous errors.
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This is because we have so far been unable to check and limit template parameters.
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For example, the following two lines of code can cause a lot of
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almost unreadable compilation errors:
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```cpp
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#include <list>
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#include <algorithm>
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int main() {
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std::list<int> l = {1, 2, 3};
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std::sort(l.begin(), l.end());
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return 0;
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}
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```
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The root cause of this code error is that `std::sort` must provide
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a random iterator for the sorting container, otherwise it will not be used,
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and we know that `std::list` does not support random access.
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In the conceptual language, the iterator in `std::list` does not satisfy
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the constraint of the concept of random iterators in `std::sort`.
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After introducing the concept, we can constrain the template parameters
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like this:
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```cpp
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template <typename T>
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requires Sortable<T> // Sortable is a concept
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void sort(T& c);
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```
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abbreviate as:
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```cpp
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template<Sortable T> // T is a Sortable typename
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void sort(T& c)
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```
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Even use it directly as a type:
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```cpp
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void sort(Sortable& c); // c is a Sortable type object
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```
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Let's look at a practical example.
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TODO:
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## Module
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TODO:
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## Contract
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TODO:
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## Range
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TODO:
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## Coroutine
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TODO:
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## Conclusion
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In general, I finally saw the exciting features of Concepts/Ranges/Modules in C++20.
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This is still full of charm for a programming language that is already in its thirties.
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[Table of Content](./toc.md) | [Previous Chapter](./09-others.md) | [Next Chapter](./appendix1.md)
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## Further Readings
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- [Why Concepts didn't make C++17？](http://honermann.net/blog/2016/03/06/why-concepts-didnt-make-cxx17/)
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- [C++11/14/17/20 Compiler Support](http://en.cppreference.com/w/cpp/compiler_support)
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- [C++ History](https://en.cppreference.com/w/cpp/language/history)
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## Licenses
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<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). |