Go - Interface value

• Real type of an interface variable is decided dynamatically
• Need be careful when comparing interface, panic will occur when real type is not comparable such as slice.
• nil value assigned to an interface variable is different from nil pointer assigned to a variable
• Ex. check is argument value nil in function sill get wrong result
• Do not assign nil pointer to interface. Because dynamic type is not nil but dynapic value is nil, cause dynamic dispatch panic