Where and Why Do I Have to Put the ‘template’ and ‘typename’ Keywords?

The typename and template keywords in C++ are useful for writing generic, flexible, reusable, and type-safe code. The typename keyword is applied to specify that a name denotes a type within the templates, and the template keyword is applied to define generic functions and classes, which helps you to develop an efficient and maintainable code. In this article, we will learn about the template and typename keywords, where they should be used, and why they should be used with the best practices.

Table of Contents:

• What is ‘template’ Keyword in C++
• What is ‘typename’ Keyword in C++
• Where to Use the template and typename Keywords in C++
• Why Use the template and typename Keywords in C++
• Conclusion

What is ‘template’ Keyword in C++

The template keyword used for the generic functions or classes that reduce code duplication in C++. To call the same function without creating any other set of classes, there is no need for code duplication, the template keyword helps the function to work with different data types.

Example:

Output:

The code shows how a template keyword is used to create a function multiply that takes two values and returns their product in the main function.

What is ‘typename’ Keyword in C++

The typename keyword in C++ is used inside templates to indicate that a name represents a type rather than a variable or function. It is required when referring to nested dependent types inside template classes to avoid ambiguity. The compiler needs typename in contexts where it must differentiate between types and non-types, especially when working with dependent types in templates

Example:

Output:

The code shows how a typename keyword with any data type T is used in a template class that uses typeid to print the type of T in the main function.

Where to Use the template and typename Keywords in C++

Here are the points from which you can find where to use the template and typename keywords in C++:

1. For the generic code that operates on different data types, you should use the template keywords.
2. You should use the typename keyword to declare the type in function and class templates in the program.
3. You must use the template keyword for the template specialization to provide the particular implementation for the particular types.
4. You must use the typename keyword in the nested classes for the nested types inside the templates to make sure that the compiler considers them as types.
5. When you are referring to dependent types inside a template, you should use the typename keyword to clarify that a name represents a type.

Why Use the template and typename Keywords in C++

Below are the important points to why to use the template and typename keywords:

1. The template keyword allows the generic code to be written once, and it can then work with data of any type, thereby providing reusability of the code without duplication.
2. The use of the template keyword assures us that all the operations are type-checked at compile time, which will be able to catch the potential errors, thereby improving the code quality.
3. The template keywords assist the creation of algorithms and data structures that easily deal with different data types, thus providing you with flexibility in writing your codes.
4. The template keyword serves towards increasing the code efficiency by the way of optimization of the code, it does not cause a run-time overhead as the template instantiation happens at compile-time.
5. The typename keyword serves to have a preference for types over non-types when dependent data types are in templates.
6. The use of the typename keyword was traditionally quite important for declaring type parameters in templates in the creation of such generic functions and classes.
7. The typename eliminates any ambiguity, such as that the compiler needs to resolve whether a name is referring to a type for its further processing.
8. The use of the typename keyword in the code enhances its readability.

Conclusion

The template and typename keywords in C++ are important for creating a reusable, flexible, and type-safe code. Use of template keyword allows you to write the generic codes, while the usage of typename keywords distinguishes between the different data types. So, understanding where and why to use these keywords is important for effective code readability and C++ programming.

Where and why do I have to put the “template” and “typename” keywords – FAQs