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Author: denevell

golang-constants-enums.md

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+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".