RefCell

A mutable memory location with dynamically checked borrow rules. You can have many immutable references or one mutable reference, but not both at the same time. The RefCell check this on runtime rather compiler time.

Concepts

• dynamically checked Dynamically means it's something happened at runtime. Statically means it's on the compiler time.
• borrowing it refers to temporarily using a reference to a memory location without taking owenership of it. Ownership in here means being responsible for managing that memory.

Defination

pub struct RefCell<T>
where
    T: ?Sized,
{ /* private fields */ }

What the Structure mean

where clause in Rust used to specify constraits on generic type parameters. since it's either sized or unsized, why need here. The Sized is default implemented, so here is relaxing it.