Difference of keywords "typename" and "class" in templates?

📝 What's the Difference Between 'typename' and 'class' in Templates?

🤔 Are you confused about the different declarations you've seen for templates, specifically the keywords 'typename' and 'class'? You're not alone! Let's dive into this topic to understand the differences and what these keywords mean in a practical example.

🤷‍♀️ What's the Difference?

At first glance, 'typename' and 'class' might seem interchangeable when defining template parameters. However, there is a subtle difference between them.

1️⃣ 'typename': The 'typename' keyword is used to declare a type parameter in a template. It indicates that the template can accept any type as an argument.

2️⃣ 'class': Similarly, the 'class' keyword can also be used to declare a type parameter in a template. It serves the same purpose as 'typename', allowing flexibility to use any type as an argument.

🤔 So, what's the distinction between 'typename' and 'class'?

The key difference lies in how they handle dependent types. When working with nested types or dependent names within a class or template, 'typename' should be used to specify that the name refers to a type. On the other hand, 'class' can be used in both cases, but it doesn't explicitly state that the name refers to a type.

Now let's uncover the meaning of these keywords in a practical example:

template <template<typename, typename> class Container, typename Type>
class Example
{
    Container<Type, std::allocator <Type>> baz;
};

🚀 Explanation of the Example:

In this example, 'Container' is a template parameter that accepts a template template argument. The 'template<typename, typename>' part indicates that the 'Container' template takes two type arguments.

The 'Type' parameter is a regular type argument. It can be any type (int, string, etc.) specified when using the 'Example' class template.

🔑 The Compelling Call-to-Action:

Templates can be confusing, but understanding the difference between keywords like 'typename' and 'class' is essential. It helps in writing more robust and flexible code.

So, next time you encounter the keywords 'typename' and 'class' in template declarations, you'll know how to use them correctly! Share this blog post with fellow developers to help them grasp this concept too.

🙌 Engage with your thoughts and questions in the comments! Let's empower each other as we explore the fascinating world of templates.