# reverse

## Category
Array

## Arity
**Unary** — `reverse <array>`.

```
reverse <array>
```

## Description
Reverses the order of elements in the array **in-place**. The array is modified directly. Returns `nil`.

## How It Works
Calls `List<Value>.Reverse()` on the underlying list. All elements are reordered. O(n) time, O(1) extra space.

## Usage

### Basic reverse
```sqf
_arr = [1, 2, 3, 4];
reverse _arr;                  // _arr is [4, 3, 2, 1]
```

### Reverse iteration
```sqf
_arr = ["a", "b", "c"];
reverse _arr;
{ systemChat _x } forEach _arr;  // prints "c", "b", "a"
```

### Palindrome check
```sqf
_isPalindrome = {
    params ["_arr"];
    _copy = +_arr;             // shallow copy
    reverse _copy;
    str _arr == str _copy
};
```

### Undo reverse
```sqf
reverse _arr;    // first reverse
// ... do work ...
reverse _arr;    // restore original order
```

> **Note**: Unlike `sort`, `reverse` does not take a direction argument — it always reverses.

## Thread Safety
**Not thread-safe**. Array must belong to the current scheduler.

## See Also
- [sort](sort.md) — sort array
- [select](select.md) — element access
- [forEach](forEach.md) — iterate array