Deduction Guides

Deduction Guides

The compiler uses special rules called “Deduction Guides” to work out the template class types. We have two types of guides:

1. compiler-generated (implicitly generated)
2. user-defined

To understand how the compiler uses the guides, let’s look at an example. Here’s a custom deduction guide[^arrded] for std::array :

[^arrded]: simplified version of libstdc++

template<typename T, typename... U>
array(T, U...) -> 
    array<enable_if_t<(is_same_v<T, U> && ...), T>, 1 + sizeof...(U)>;