Nim by Example: Tables

Tables are Nim's key-value collections (also known as maps or dictionaries in other languages).
Also see Nim's documentation of table module.
To use tables, we import the tables module.
import tables
To create an empty table, call initTable proc, specifying key and value types.
var fruit_prices = initTable[string, int]()
Add/set key-value pair to table.
fruit_prices["apple"] = 75
fruit_prices["kiwi"] = 60
fruit_prices["banana"] = 45
echo fruit_prices
Existance of a key can be checked with hasKey proc.
echo "kiwi? ", fruit_prices.hasKey("kiwi")
A key value pair can be removed by calling del proc.
echo fruit_prices
Use len proc to get number of pairs in the table.
echo "pairs #: ", fruit_prices.len
A table can also be initialized with values directly.
var numbers = {1: "one", 2: "two", 3: "three"}.toTable
echo numbers
Table's key-value pairs can be iterated using for loop.
for fruit, price in fruit_prices:
    echo fruit, " costs ", price
Reassinging a table will make a copy of it!
var numbers2 = numbers
numbers.del(1) # not removed from numbers2
echo numbers
echo numbers2
To work with references instead of values, use TableRef type instead of Table. TableRef can be created with newTable proc.
var letters = newTable[char, string]()
letters['a'] = "first"
letters['b'] = "second"
var letters2 = letters
letters.del('b') # also removed from letters2
echo letters
echo letters2
Later on, in references example, we will learn more about working with references.
$ nim c -r tables1.nim
{"kiwi": 60, "apple": 75, "banana": 45}
kiwi? true
{"kiwi": 60, "apple": 75}
pairs #: 2
{1: "one", 2: "two", 3: "three"}
kiwi costs 60
apple costs 75
{2: "two", 3: "three"}
{1: "one", 2: "two", 3: "three"}
{'a': "first"}
{'a': "first"}

Previously: Sequences
Next up: Procedures