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I am trying to use enum in golang as below. I am struggling to find a easy way to iterate over the list of constant values. What are common practice in golang to iterate over constant values used as enum. Thanks!
type DayOfWeek int const( Monday DayOfWeek = iota Tuesday Wednesday Thursday Friday Saturday Sunday ) In Java, we can iterate as below.
public enum DayOfWeek { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY } for (DayOfWeek day: DayOfWeek.values()) { // code logic } 
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Enums are lists of constants. When you need a predefined list of values which do represent some kind of numeric or textual data, you should use an enum. You should always use enums when a variable (especially a method parameter) can only take one out of a small set of possible values.
Enums limit you to the required set of inputs whereas even if you use constant strings you still can use other String not part of your logic. This helps you to not make a mistake, to enter something out of the domain, while entering data and also improves the program readability.
The enum type, introduced in Java 5, is a special data type that represents a group of constants. Using enums, we can define and use our constants in the way of type safety. It brings compile-time checking to the constants.
C++ Enumeration Iteration over an enumThere is no built-in to iterate over enumeration.
Iterate over Enum Values: There are many ways to iterate over enum values: Iterate Using forEach() Iterate Using for Loop. Iterate Using java.util.stream. Iterate Using forEach(): The forEach() method works on list or set. For using forEach() method, convert enum into list or set.
This method returns an array containing all the values. Once you obtain the array you can iterate it using the for loop. Following java program iterates the contents of the enum Days created above, using the for loop −
An enum can contain constants, methods etc. Given below is a demonstration on how to declare an enum: Iterate over Enum Values: There are many ways to iterate over enum values: Iterate Using forEach(): The forEach() method works on list or set. For using forEach() method, convert enum into list or set.
You can convert the enum into a list or set and perform required actions on each element of the list using the forEach () method. Following java program converts the enum Days created above into a set and, iterates its contents using forEach loop − You can use foreach loop with streams too.
There is no direct way to enumerate the values/instances of named type at runtime, whether variables or constants, unless you specifically define a slice that lists them. This is left up to the definer or the user of the enumeration type.
package main import ( "fmt" "time" ) var Weekdays = []time.Weekday{ time.Sunday, time.Monday, time.Tuesday, time.Wednesday, time.Thursday, time.Friday, time.Saturday, } func main() { for _, day := range Weekdays { fmt.Println(day) } } In order be able to generate this list dynamically at runtime, e.g. via reflection, the linker would have to retain all the symbols defined in all packages, like Java does. The golang-nuts group discussed this, regarding names and functions exported from a package, a superset of package constant definitions. https://groups.google.com/forum/#!topic/golang-nuts/M0ORoEU115o
It would be possible for the language to include syntactic sugar for generating this list at compile time if and only if it were referenced by the program. What should the iteration order be, though? If your week starts on Monday the list I defined is not very helpful; you will have to define your own slice to range through the days from Monday to Sunday.
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You can do that without reflection.
First execute the Go tools Stringer at compile time using go generate. This creates a file [filename]_string.go which contains a map _[structname]_map of enum values referencing enum variable names as strings. This map is private, so simply assign it to a public map upon package initialization.
var EnumMap map[Enum]string func init() { EnumMap = _Enum_map } type Enum uint //go:generate go run golang.org/x/tools/cmd/stringer -type=Enum const ( One Enum = iota Two ) Then you can simply loop over the keys of the map.
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