Collections

Arrays

The array type is a list of elements of the same type and the size does not change, so must be defined at compile time:

var a: array[2, int] = [3, 2]

Just as with basic variable types, the type can often be inferred:

var a = [3, 2]

If we don’t know the value, but still want to define it, we can declare it with the type and size:

var a: array[3, char]

Indexes

As with most programming languages, referencing an index in an array, starts at 0:

var a: array = ['a', 'b', 'c','d']
echo("The first element of the array is ", a[0])

We can set a custom index range as well:

var 
  customArrayAlpha: array[-6 .. -3, char] = ['a', 'b', 'c', 'd']
  customArrayInt: array[-3 .. 0, int] = [1, 2, 3, 4]

echo customArrayAlpha[-5] # output the second element
echo customArrayInt[-1] # output the third element

There is a prefix that can be used to target the last part of the array, so to get the last element, use ^ as a prefix:

var a: array = ['a', 'b', 'c','d']
echo("The last element of the array is ", a[^1])

Slicing

We can use a start .. stop syntax to get a range of values in an array:

var a: array = ['a', 'b', 'c','d']
echo("Elements 0 to 2 in the array are ", a[ 0 .. 2])

Sequences

Sequences are dynamic in size and can grow as needed, there are two ways to define a new sequence:

var 
  sequenceA: seq[char] = @['a', 'b'] # to initialize with actual values
  sequenceB = newSeq[char](2) # use this if size known ahead of time, as it is more efficient

To add to the sequence without a defined size, we use add to assign a value:

var openSequence: seq[char] = @[]
openSequence.add('c')

To add to the sequence with a defined size, we would reference the index to add a value:

var knownSizeSequence: seq[int] = newSeq[int](2) 
knownSizeSequence[0] = 2
knownSizeSequence[1] = 3

Sequence Length

To get the sequence length, you can use the len syntax:

var sequenceNum = @[4, 5, 6]
echo sequenceNum.len # outputs 3

Sets

Sets are an ordinal type (only accepts values that can be counted) and must each value must be unique. It can include char, int8, int16, enum, and unit8 for example.

var charSet: set[char]
charSet = {'a', 'e', 'c', 'd'}

The order of the items being stored are not kept track of, so we cannot use an index to get a value, but can use the in keyword to see if a value is in the set:

var charSet: set[char]
charSet = {'a', 'e', 'c', 'd'}
echo 'c' in charSet # outputs true