After the Swift statement a=b is executed, for each one of the following statements, explain whether it is always incorrect, whether it may be sometimes correct, and if so, which data types would be those variables, or whether it may be always correct.

1. Variables a and b are same;

2. The value of b is assigned to variable a but if b changes later, it will not affect the value of variable a;

3. The value of b is assigned to variable a but if b changes later, it will affect the value of variable a;

4. The value of variable a is assigned to variable b, and the value of variable b is assigned to variable a;