Szathmáry László honlapja @ DEIK

In Nim, enums are ordinal types. They have an order, they can be used in case statements, and they can serve as the base type of sets.

Normal enums

Under normal I mean non-pure enums.

type
Color = enum
colRed,
colGreen,
colBlue

let
color1: Color = colRed

color2 = colGreen # can be used alone

color3 = Color.colBlue # can be prefixed with the name of the enum

echo color1 # colRed
echo color2 # colGreen
echo color3 # colBlue

Since these enum values are usually used alone, it's a good idea to give a prefix to these values. Thus, for instance, instead of "green", the value should be called "colGreen". Now, when you see "colGreen" in your code, you'll see that it's an enum value, and it's a color.

Pure enums

type
Color {.pure.} = enum # !!! {.pure.} pragma is used !!!
red, green, blue

let
color1: Color = Color.red

#color2 = green # error: cannot be used alone

color3 = Color.blue # MUST be prefixed with the name of the enum

echo color1 # red
echo color3 # blue

Notice the usage of the pure pragma! It tells the compiler that an enum's value cannot be used alone. The enum's value MUST be prefixed with the name of the enum.

From the manual: "An enum type can be marked as pure. Then access of its fields always requires full qualification."

Assigning values to enum members

type
Direction = enum
dirUp = "up",
dirRight = "right",
dirDown = "down",
dirLeft = "left"

echo dirUp # up
echo dirUp.typeOf # Direction

echo $dirUp # "up", as string
echo ($dirUp).typeOf # string

echo ord(dirUp) # 0
echo ord(dirRight) # 1

𝥶Here we assign string values to enum members.

You can also assign integer values to enums:

type
Status = enum
sOk = 200,
sNotFound = 404,
sError = 500

echo sOk # sOk
echo sOk.typeOf # Status

echo $sOk # "sOk" , as string

echo ord(sOk) # 200

Or even both at once:

type
Direction = enum
dirUp = (1, "up"),
dirRight = "right", # dirRight = (2, "right"),
dirDown = "down", # etc.
dirLeft = "left"

echo dirUp # up
echo dirUp.typeOf # Direction

echo $dirUp # "up", as string
echo ($dirUp).typeOf # string

echo ord(dirUp) # 1
echo ord(dirRight) # 2
echo ord(dirDown) # 3
echo ord(dirLeft) # 4

Get the symbol's name

import std/enumutils # !!! import this

type
Direction = enum
dirUp = (1, "up"),
dirRight = "right",

echo symbolName(dirUp) # "dirUp" , as string