golang-constants-enums.md

Title: Golang: Constants, enums and iota Tags: golang

You can type or untype your constants. And untyped constant can be used in any expression and converted implicitly:

	const thing = 5 // untyped
	const thing2 int = 5 // typed - only used in int expressions

Enums come by putting a bunch of consts in parens:

	const ( 
		One = 1
		Two = 2
		Three = 4
	)

You can use iota to create these values. Within a const group, it starts at 1, and then increments for each expression.

	const ( 
		One = 1 << iota // 1 (i.e. 1 << 1)
		Two // 2 (i.e. 1 << 2)
		Three // 4 (i.e 1 << 3)
	)

If you print a Two, for example, it will display 2.

You can 1) Give the enum a custom type and 2) give the custom type a String() method to change that:

Giving custom types methods is the OOP of golang. And will be discussed in later posts.

	type Type int

	const ( 
		One Type = 1 << iota // 1
		Two Type // 2 (i.e. 1 << 2)
		Three Type // 4 (i.e 1 << 3)
	)

	func (t Type) String() string {
		s:=""
		if t&One==One {
			s+="One"
		}
		...
		return s
	}

Now if you print the 'One' type it will out the text "One".