any-en.md

Any

The Any type provides generic object operations after type erasure. It represents an object of any type but cannot represent references and pointers.

In other words, Any holds the value of an object, not its memory address. Therefore, consider the following examples:

Foo foo;

// If moveable, the move constructor will be called. Otherwise, the copy constructor will be called.
Any any(zeno::reflect::move(foo));

// The copy constructor will always be called.
Any any(foo);

Note that in the examples above, if the type cannot be copy-constructed or move-constructed, or if there is a compatible implicit conversion constructor, it will result in a compilation error.

Therefore, we provide a make_any method to construct an Any object in-place.

// Assume Foo has a constructor with three int parameters
Any any = zeno::reflect::make_any<Foo>(123, 456, 789);

Move and Copy

As mentioned above, if Any is passed by value:

Any origin_any = make_any<Foo>();

// This triggers the copy constructor to clone the internal value.
// If copy construction is not possible, an exception will be thrown.
Any duplicated_any = origin_any;

If you do not want to trigger the clone operation, you need to pass it by pointer, reference, or using move semantics.