如何在Go中创建键值的枚举/映射

Question

I am new to Go and love it so far but it seems that I cannot find a simple solution to this.

I want to create a constant that I can reference in my code by Key and get its value

I have this:

const (
    DBName            = "goApi"
    UsersTable string = "users"
)

And would like to have a Tables constant variable that stores the value

Example:

var Tables = {
   UsersTable : "users",
   PostsTable : "posts"
}

//Somewhere else in the code
fmt.Println(Tables.UsersTable) //output "users"

How can I achieve this in Go?

Answer 1

What you can declare as const in Go is limited to only the basic types like ints, strings, bools, etc. There is no way to declare non-basic types like structs, maps, slices, funcs, etc. as a const.

So to get to Tables.UsersTable you can either declare your Tables as a struct var:

var Tables = struct{
    UsersTable string
    PostsTable string
}{
    UsersTable: "users",
    PostsTable: "posts",
}

Note that since this is a variable and not a constant, there's nothing that protects the fields' values from being modified by malice or bug.

Or, the other option you have is to create a new package, name it tables, and in it declare your constants.

package tables

const (
    UsersTable = "users"
    PostsTable = "posts"
)

Then you can use it by simply importing the package

import (
    "fmt"
    "path/to/tables"
)

func main() {
    fmt.Println(tables.UsersTable)
}

Note that the first solution, if imported by another package will result in fmt.Println(somepkg.Tables.UsersTable) (unless a . import is used) which may not be what you're looking for, or maybe it is.