How Does C 17's `template ` Enhance Template Parameter Usage?

Unlocking the Potential of Template Auto: Advantages in C 17

The introduction of template in C 17 has brought significant advantages to template parameters, expanding their versatility and offering new possibilities for code development.

Natural Extension of Auto for Template Instantiation

auto has been widely adopted for variable declarations, providing type deduction based on the assigned value. The extension of auto to template parameters further simplifies template instantiation by automatically determining the type of the parameter from its value. This eliminates the need for explicit type specification, offering a more concise and intuitive syntax.

Convenient and Explicit Type Deduction

The use of auto in template parameters enables type deduction even for non-type template parameters. For example, previously, the following constant template required verbose type declarations:

template <typename Type, Type value>
constexpr Type constant = value;

With template , this can be simplified to:

template <auto value>
constexpr auto constant = value;

The compiler now automatically infers the type from the value assigned to value, making the code more readable and less error-prone.

Enhanced Variadic Template Handling

template proves particularly beneficial for variadic template parameters. In pre-C 17, writing a heterogeneous value list required complex workarounds. However, with auto, the following elegant syntax is now possible:

template <auto ... vs>
struct HeterogenousValueList {};

using MyList1 = HeterogenousValueList<42, 'X', 13u>;

Similarly, homogenous value lists can be written succinctly:

template <auto v0, decltype(v0) ... vs>
struct HomogenousValueList {};

using MyList2 = HomogenousValueList<1, 2, 3>;

Conclusion

template in C 17 not only extends the functionality of auto to template parameters, but also introduces new possibilities for concise and expressive code development. It enhances type deduction, simplifies variadic template handling, and makes code more readable and maintainable. These advantages make template a valuable tool for modern C programming.

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