The kind traits
Rust types can be classified in various useful ways according to intrinsic properties of the type. These classifications, often called 'kinds', are represented as traits.
They cannot be implemented by user code, but are instead implemented by the compiler automatically for the types to which they apply.
The 4 kinds are
Copy - types that may be copied without allocation. This includes scalar types and managed pointers, and exludes owned pointers. It also excludes types that implement Drop.
Send - owned types and types containing owned types. These types may be transferred across task boundaries.
Freeze - types that are deeply immutable.
Copy types include both implicitly copyable types that the compiler will copy automatically and non-implicitly copyable types that require the copy keyword to copy. Types that do not implement Copy may instead implement Clone.
CopyFreezeSendSized