visit in C++17 | std::visit In C++17
std::visit is a utility function introduced in C++17 as part of the variant header. It provides a way to apply a callable (such as a function object or lambda) to the alternative types contained within a std::variant object.
Here's a recap of std::visit and how it works:
1. Variant Types: A std::variant is a type-safe union that can hold values of different types. Only one value among its alternative types can be active at any given time.
2. Applying a Callable: std::visit allows you to apply a callable to the currently active alternative type stored in a std::variant object. The callable can be a function object, a lambda function, or any other callable object.
3. Dispatching to Appropriate Function: When you call std::visit with a callable and a std::variant object, it internally dispatches to the appropriate function or lambda based on the currently active alternative type in the variant object.
4. Handling All Alternative Types: You need to provide an overload for the callable for each alternative type stored in the std::variant object. std::visit ensures that the appropriate overload is called based on the active alternative type.
5. Compile-Time Type Checking: std::visit provides compile-time type checking to ensure that all alternative types are handled correctly. If there's no appropriate overload for the active alternative type, it results in a compilation error.
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