Complex variable types in nim

advanced_types.nim

#Type with enum
type
  Direction = enum
    north, east, south, west

var x = south     # `x` is of type `Direction`; its value is `south`
echo x            # writes "south" to `stdout`

#Subrange
type
  MySubrange = range[0..5]
  
#Set
type
  CharSet = set[char]
var
  x: CharSet
x = {'a'..'z', '0'..'9'} # This constructs a set that contains the
                         # letters from 'a' to 'z' and the digits
                         # from '0' to '9'
                         
#Bit Fields
type
  MyFlag* {.size: sizeof(cint).} = enum
    A
    B
    C
    D
  MyFlags = set[MyFlag]

proc toNum(f: MyFlags): int = cast[cint](f)
proc toFlags(v: int): MyFlags = cast[MyFlags](v)

assert toNum({}) == 0
assert toNum({A}) == 1
assert toNum({D}) == 8
assert toNum({A, C}) == 5
assert toFlags(0) == {}
assert toFlags(7) == {A, B, C}

#Arrays
type
  IntArray = array[0..5, int] # an array that is indexed with 0..5
var
  x: IntArray
x = [1, 2, 3, 4, 5, 6]
for i in low(x)..high(x):
  echo x[i]
  
type
  Direction = enum
    north, east, south, west
  BlinkLights = enum
    off, on, slowBlink, mediumBlink, fastBlink
  LevelSetting = array[north..west, BlinkLights]
var
  level: LevelSetting
level[north] = on
level[south] = slowBlink
level[east] = fastBlink
echo repr(level)  # --> [on, fastBlink, slowBlink, off]
echo low(level)   # --> north
echo len(level)   # --> 4
echo high(level)  # --> west

type
  LightTower = array[1..10, LevelSetting]
var
  tower: LightTower
tower[1][north] = slowBlink
tower[1][east] = mediumBlink
echo len(tower)     # --> 10
echo len(tower[1])  # --> 4
echo repr(tower)    # --> [[slowBlink, mediumBlink, ...more output..
# The following lines don't compile due to type mismatch errors
#tower[north][east] = on
#tower[0][1] = on

#Sequences
var
  x: seq[int] # a reference to a sequence of integers
x = @[1, 2, 3, 4, 5, 6] # the @ turns the array into a sequence allocated on the heap

#Open Arrays
var
  fruits:   seq[string]       # reference to a sequence of strings that is initialized with '@[]'
  capitals: array[3, string]  # array of strings with a fixed size

capitals = ["New York", "London", "Berlin"]   # array 'capitals' allows assignment of only three elements
fruits.add("Banana")          # sequence 'fruits' is dynamically expandable during runtime
fruits.add("Mango")

proc openArraySize(oa: openArray[string]): int =
  oa.len

assert openArraySize(fruits) == 2     # procedure accepts a sequence as parameter
assert openArraySize(capitals) == 3   # but also an array type

#Varargs
proc myWriteln(f: File, a: varargs[string]) =
  for s in items(a):
    write(f, s)
  write(f, "\n")

myWriteln(stdout, "abc", "def", "xyz")
# is transformed by the compiler to:
myWriteln(stdout, ["abc", "def", "xyz"])

#Slices
var
  a = "Nim is a programming language"
  b = "Slices are useless."

echo a[7 .. 12] # --> 'a prog'
b[11 .. ^2] = "useful"
echo b # --> 'Slices are useful.'

#Objects
type
  Person = object
    name: string
    age: int

var person1 = Person(name: "Peter", age: 30)

echo person1.name # "Peter"
echo person1.age  # 30

var person2 = person1 # copy of person 1

person2.age += 14

echo person1.age # 30
echo person2.age # 44


# the order may be changed
let person3 = Person(age: 12, name: "Quentin")

# not every member needs to be specified
let person4 = Person(age: 3)
# unspecified members will be initialized with their default
# values. In this case it is the empty string.
doAssert person4.name == ""

#Exported object
type
  Person* = object # the type is visible from other modules
    name*: string  # the field of this type is visible from other modules
    age*: int
    
#Tuples
type
  # type representing a person:
  # A person consists of a name and an age.
  Person = tuple
    name: string
    age: int
  
  # Alternative syntax for an equivalent type.
  PersonX = tuple[name: string, age: int]
  
  # anonymous field syntax
  PersonY = (string, int)

var
  person: Person
  personX: PersonX
  personY: PersonY

person = (name: "Peter", age: 30)
# Person and PersonX are equivalent
personX = person

# Create a tuple with anonymous fields:
personY = ("Peter", 30)

# A tuple with anonymous fields is compatible with a tuple that has
# field names.
person = personY
personY = person

# Usually used for short tuple initialization syntax
person = ("Peter", 30)

echo person.name # "Peter"
echo person.age  # 30

echo person[0] # "Peter"
echo person[1] # 30

# You don't need to declare tuples in a separate type section.
var building: tuple[street: string, number: int]
building = ("Rue del Percebe", 13)
echo building.street

# The following line does not compile, they are different tuples!
#person = building
# --> Error: type mismatch: got (tuple[street: string, number: int])
#     but expected 'Person'

#Reference object
type
  Node = ref object
    le, ri: Node
    data: int
var
  n: Node
new(n)
n.data = 9
# no need to write n[].data; in fact n[].data is highly discouraged!