Gain insights into C++20 Concepts to enhance type safety. Delve into creating compiler-checked criteria for templates and improving error clarity for seamless generic code development.

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c++20

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This course will walk you through the newest version of C++ 20, C++ Concepts.

You will go through one of the most significant new features in C++20, which is Concepts. Concepts allow you to create compiler-checked criteria for template parameters, revolutionizing the way you think about and develop generic code. You can use them to provide both syntactic and semantic requirements. They also allow you to explicitly express your goal in the type system. If something goes wrong, you'll get a clear error message from the compiler.

While useful, Concepts can be difficult to apply and even confusing sometimes. This course provides you with the knowledge you need to overcome these obstacles and move on to more complex topics.

Let's get started.

C++ Concepts: Improve Type Safety with C++ 20

## Require a nested type
Just like for the nested types, we have to use the keyword `typename` along with the specialized class template that is expected to be a valid specialization:

```c++
template<typename T>
concept TypeRequirement = requires {
    typename Other<T>;
};
```

In this case, the concept `TypeRequirement` requires that the class template `Other` can be instantiated with `T`.
Let’s see how it works.

## Declare a class template
 We declare a class template `Other` and make a requirement on the template parameter by making sure that `Other` cannot be instantiated with a `vector` of `int` values.

```c++
template <typename T>
requires (!std::same_as<T, std::vector<int>>) // parentheses are mandatory!
struct Other{};
```

Now, the line `TypeRequirement auto myVec = std::vector<int>{1, 2, 3};` fails. Compile the following code to see the error. 


# Require a nested type
Just like for the nested types, we have to use the keyword `typename` along with the specialized class template that is expected to be a valid specialization:

```c++
template<typename T>
concept TypeRequirement = requires {
    typename Other<T>;
};
```

In this case, the concept `TypeRequirement` requires that the class template `Other` can be instantiated with `T`.
Let’s see how it works.

# Declare a class template
 We declare a class template `Other` and make a requirement on the template parameter by making sure that `Other` cannot be instantiated with a `vector` of `int` values.

```c++
template <typename T>
requires (!std::same_as<T, std::vector<int>>) // parentheses are mandatory!
struct Other{};
```

Now, the line `TypeRequirement auto myVec = std::vector<int>{1, 2, 3};` fails. Compile the following code to see the error. 


Get an overview of how a class template specialization should name a type.

Introduction

The Concept Behind C++ Concepts

Four Ways to use Concepts in Functions

C++ Concepts with Classes

Concepts Shipped with the C++ Standard Library

How to Write Your Own C++ Concepts

How to Use C++ Concepts in Real Life

Summary

A Class Template Specialization

Require a nested type

Declare a class template