How to declare a constant map in Golang

Question

I am trying to declare to constant in Go  but it is throwing an error  Could anyone please help me with the syntax of declaring a constant in Go   This is my code    const romanNumeralDict map int string       1000   M     900    CM     500    D     400    CD     100    C     90     XC     50     L     40     XL     10     X     9      IX     5      V     4      IV     1      I       This is the error    command-line-arguments   Roman Numerals go 9  syntax error  unexpected

User · Answer

As stated above to define a map as constant is not possible. But you can declare a global variable which is a struct that contains a map.

The Initialization would look like this:

var romanNumeralDict = struct {
    m map[int]string
}{m: map[int]string {
    1000: "M",
    900: "CM",
    //YOUR VALUES HERE
}}

func main() {
    d := 1000
    fmt.Printf("Value of Key (%d): %s", d, romanNumeralDict.m[1000])
}

User · Answer

You may emulate a map with a closure   package main  import        fmt        http   stackoverflow com a 27457144 10278  func romanNumeralDict   func int  string          innerMap is captured in the closure returned below     innerMap    map int string          1000   M           900    CM           500    D           400    CD           100    C           90     XC           50     L           40     XL           10     X           9      IX           5      V           4      IV           1      I              return func key int  string           return innerMap key           func main         fmt Println romanNumeralDict   10       fmt Println romanNumeralDict   100        dict    romanNumeralDict       fmt Println dict 400       Try it on the Go playground

User · Answer

Your syntax is incorrect   To make a literal map  as a pseudo-constant   you can do   var romanNumeralDict   map int string    1000   M     900    CM     500    D     400    CD     100    C     90     XC     50     L     40     XL     10     X     9      IX     5      V     4      IV     1      I       Inside a func you can declare it like   romanNumeralDict    map int string        And in Go there is no such thing as a constant map   More information can be found here   Try it out on the Go playground

User · Answer

And as suggested above by Siu Ching Pong -Asuka Kenji with the function which in my opinion makes more sense and leaves you with the convenience of the map type without the function wrapper around         romanNumeralDict returns map int string dictionary  since the return           value is always the same it gives the pseudo-constant output  which           can be referred to in the same map-alike fashion         var romanNumeralDict   func   map int string   return map int string               1000   M               900    CM               500    D               400    CD               100    C               90     XC               50     L               40     XL               10     X               9      IX               5      V               4      IV               1      I                                  func printRoman key int              fmt Println romanNumeralDict   key                      func printKeyN key  n int              fmt Println strings Repeat romanNumeralDict   key   n                      func main               printRoman 1000            printRoman 50            printKeyN 10  3              Try this at play golang org

User · Answer

You can create constants in many different ways   const myString    hello  const pi   3 14    untyped constant const life int   42    typed constant  can use only with ints    You can also create a enum constant   const       First   1    Second   2    Third   4     You can not create constants of maps  arrays and it is written in effective go      Constants in Go are just that   constant  They are created at compile   time  even when defined as locals in functions  and can only be   numbers  characters  runes   strings or booleans  Because of the   compile-time restriction  the expressions that define them must be   constant expressions  evaluatable by the compiler  For instance  1 lt  lt 3   is a constant expression  while math Sin math Pi 4  is not because the   function call to math Sin needs to happen at run time

[go] How to declare a constant map in Golang?

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