For struct fields, sometimes we want to control the accessibility of the fields, so they are only accessible within the struct methods.

For example:

struct Room {
	pub beds: Field, // public
        size: Field // private
}

Uint8.update_size(self, size: Field) {
        self.size = size; 
}

fn main() {
       let room = Room {beds: 2, size: 10};
       uint.beds = 2; // allowed
       uint.size = 5;  // not allowed
       uint.update_size(5); // allowed
}

When there is a pub attribute for a struct field, the field can be accessible from external. Otherwise, the private fields are only accessible in the struct methods.