is swift closure a value or reference type

In Swift, closures are treated as reference types. This is because closures can capture and store references to variables and constants from their surrounding context. When a closure captures a variable, it captures it by reference, allowing changes to the variable to be observed in the original scope and vice versa. This behavior is particularly important for escaping closures, where the closure might outlive the scope in which it was created, necessitating heap allocation and memory management through reference counting.

For non-escaping closures, the context can be allocated on the stack, and the closure does not need to be memory managed beyond the scope of its call. However, for escaping closures, the context must be heap allocated and managed with retains and releases, similar to an instance of an anonymous Swift class.

For more details, you can refer to the session Explore Swift performance (28:11).