# Array

Arrays are the most basic __collection (aggregate)__.
A collection is an object that can hold multiple objects inside it.

```python
a = [1, 2, 3]
a: [Int; 3] # Type specification: number after semicolon is the number of elements
# Can be omitted if the number of elements is not known
a: [Int]

mut_a = [!1, !2, !3]
mut_a[0].inc!()
assert mut_a == [2, 2, 3]
```

As a rule, arrays cannot contain objects of different types.

```python,compile_fail
[1, "a"] # TypeError: 1st element is Int, but 2nd element is Str
```

However, you can bypass the restriction by explicitly specifying the type like this.

```python
[1: Int or Str, "a"]
```

## Slice

An array can also have multiple values taken out at once. This is called slicing.

```python
l = [1, 2, 3, 4]
# Same as l[1:3] in Python
assert l[1.. <3] == [2, 3]
assert l[1..2] == [2, 3]
# Same as l[1]
assert l[1..1] == [2]
# Same as l[::2] in Python
assert l[..].step(2) == [2, 4]
```

The object obtained by slicing is an (immutable) copy to an array.

```python
print! Typeof l[1..2] # [Int; 4]
```

<p align='center'>
    <a href='./09_builtin_procs.md'>Previous</a> | <a href='./11_dict.md'>Next</a>
</p>
