Templates recap

Excellent work! You've mastered the fundamentals of templates in C++. Let's review the key concepts from this section.

Templates and Generic Programming

Templates enable you to write generic code that works with any type, eliminating the need to duplicate logic for different data types. By using placeholder types (template type parameters) or compile-time values (non-type parameters), you can create functions and classes that adapt to various use cases.

Template Instantiation

Template functions and classes are not compiled until they are instantiated with specific types. When you use a template with a particular type, the compiler generates a concrete version (an instance) of that template. This process is called instantiation.

Template Definitions in Header Files

When defining template classes, the standard approach is to place the entire definition and all member function implementations in a header file. Unlike regular classes, splitting template definitions from implementations across separate files causes linker errors because templates are instantiated on-demand per translation unit.

Template Specialization

Template specialization provides fine-grained control over template behavior for specific types. Full specialization replaces all template parameters with concrete types, while partial specialization (available only for classes) replaces some parameters while keeping others generic. This allows optimizations like bit-packing for bool or custom behavior for pointer types.

Standard Library Containers

The C++ Standard Library makes extensive use of templates for its container classes. Templates like std::vector, std::array, std::map, and std::queue demonstrate how templates enable type-safe, reusable containers. Writing container classes is one of the primary use cases for templates.

Key Terminology

  • Template: Code pattern that works with multiple types
  • Template type parameter: Placeholder type in a template
  • Non-type parameter: Compile-time value parameter in a template
  • Instantiation: Process of generating concrete code from a template
  • Instance: Concrete version of a template for a specific type
  • Template specialization: Custom implementation for specific types
  • Full specialization: Specialization with all template parameters specified
  • Partial specialization: Specialization with some template parameters still generic
  • Container class: Class that holds collections of objects

Looking Forward

Templates are a powerful feature that enables code reuse and type safety in C++. The concepts you've learned—generic programming, instantiation, specialization—form the foundation for understanding the Standard Library and writing your own reusable components. Practice applying templates to solidify your understanding and recognize when generic solutions are appropriate.