Errors and Assertions

Using static_assert in Template Code

The lesson shows an example of using static_assert() with std::is_floating_point to validate template parameters. What are some other common type traits I can use for template validation?

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static_assert() is extremely useful in template code for validating template parameters at compile-time. It allows you to provide clearer error messages and avoid instantiating invalid template specializations.

Here are some common type traits from the <type_traits> header that are useful for template validation:

Example 1: std::is_integral and std::is_floating_point:

template <typename T>
T sum(T a, T b) {
  static_assert(std::is_integral<T>::value ||
                "sum() requires numeric types");
  return a + b;

Example 2: std::is_base_of:

template <typename T>
class Derived : public T {
  static_assert(std::is_base_of<Base, T>::value,
                "T must be derived from Base");
  // ...

Example 3: std::is_same:

template <typename T, typename U>
void assert_same() {
  static_assert(std::is_same<T, U>::value,
                "Types must be the same");

Example 4: std::is_pointer and std::is_reference:

template <typename T>
void process(T t) {
                "Pointers are not allowed");
                "References are not allowed");
// ...

Example 5: std::is_constructible:

template <typename T, typename... Args>
void construct(Args&&... args) {
  static_assert(std::is_constructible<T, Args...>::value,
                "T must be constructible from Args");
  T obj(std::forward<Args>(args)...);
// ...

These are just a few examples. The <type_traits> library provides many more type traits for checking properties like const-qualification, volatility, trivial constructibility, default constructibility, and more.

In C++17 and later, you can use the _v suffixed versions of the type traits for a more concise syntax:

template <typename T>
void foo(T t) {
                "foo() requires an integral type");
  // ...

Using type traits with static_assert in your template code can lead to more expressive and self-documenting interfaces, as well as clearer error messages for users of your templates.

Answers to questions are automatically generated and may not have been reviewed.

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