C++: What is std::any?

std::any — type-erased container for any value.

1#include <any>
2std::any a = 42;
3std::any b = std::string("hello");
4
5// Retrieve
6if (a.type() == typeid(int)) {
7    int val = std::any_cast<int>(a);
8}
9
10// Safe cast (returns nullptr on failure)
11int* p = std::any_cast<int>(&a);

Use cases:

• Dynamic property bags
• Heterogeneous containers
• Plugin systems

Alternatives:

• std::variant for known types (faster)
• void* for C-style (unsafe)
• Templates for compile-time polymorphism

When to use:

• Type truly unknown at compile time
• Don't know types at design time
• Performance not critical