In this section, we'll discuss some of the advanced traits that are important to know when we are dealing with complex code bases.
Advanced traits
Sized and ?Sized
The Sized trait is a marker trait that represents types whose sizes are known at compile time. It is implemented for most types in Rust except for unsized types. All type parameters have an implicit trait bound of Sized in their definition. We can also specify optional trait bounds using the ? operator before a trait, but the ? operator with traits only works for marker traits as the time of writing this book. It may be extended to other types in future.
