Struct and its Abilities

Struct is a way of defining custom type in move. It can be described as a simple key-value storage where key is a name of property and value is what's stored.

Syntax:

struct NAME has Abilities
{
    FIELD1 : TYPE1,
    FIELD2 : TYPE2,
    ...
}

Struct can have up to 4 abilities which define how values of this type can be used, dropped or stored.

• Copy - value can be copied (or cloned by value).

• Drop - value can be dropped by the end of scope.

• Key - value can be used as a key for global storage operations.

• Store - value can be stored inside global storage.

Abilities for Primitive types like integers, vector, addresses and boolean are pre-defined and unchangeable : copy, drop and store.

module my_addrx::Application {
	use std::vector;
        use std::debug;
	use std::string::{String,utf8};

	struct Users has key,drop {
		list_of_users: vector<User>    //storing the list of the users
	}

	struct User has store,drop,copy {
		name:String,                   //information required for a typical user
		age:u8
	}

        //creating a user by adding the user to the existing list and returning the user
	public fun create_user(newUser: User,users: &mut Users): User{
		vector::push_back(&mut users.list_of_users,newUser);
		return newUser
	}
	
	#[test]
	fun test_create_friend(){
		let user1 = User {
			name:utf8(b"Tony"),
			age:50,
		};
		
        let users = Users{
			list_of_users: vector::empty<User>()
		};

		let createdUser = create_user(user1,&mut users);
        debug::print(&users);
        assert!(createdUser.name == utf8(b"Tony"),0);
	}
}