# set

## Category
HashMap / Array / Shared

## Arity
**Binary** — `<target> set [key|index, value]`.

```
<hashmap> set [key, value]
<array> set [index, value]
<shared> set [nil, value]    // write shared value
```

## Description
Multi-purpose assignment command. Packs parameters into an array on the right side:

- **HashMap**: `_map set [key, value]` — stores a key-value pair. Creates key if not present, overwrites if exists.
- **Array**: `_arr set [index, value]` — sets element at index. Index must be within bounds.
- **Shared**: `_shared set [nil, value]` — writes a value to a shared (atomic) variable. Not atomic — prefer [compareSwap](compareSwap.md) for concurrent updates.

## How It Works
The host dispatches based on the left operand type, unpacks the right-side array, and performs the appropriate write operation.

## Usage

### HashMap set
```sqf
_map = createHashMap;
_map set ["health", 100];
_map set ["name", "player"];
_map set ["health", 75];       // overwrite existing key
```

### Array set
```sqf
_arr = [1, 2, 3, 4];
_arr set [0, 99];              // _arr is [99, 2, 3, 4]
_arr set [3, 88];              // _arr is [99, 2, 3, 88]

// Out of bounds → error
_arr set [99, 0];              // ERROR — index out of range
```

### Shared set
```sqf
shared _flag = false;
_flag set [nil, true];         // set shared value (not atomic!)
// Better for concurrent updates:
_flag compareSwap [false, true];
```

### Bulk hashmap population
```sqf
_config = createHashMap;
{
    _x params ["_key", "_val"];
    _config set [_key, _val];
} forEach [
    ["volume", 0.8],
    ["music", true],
    ["difficulty", "normal"]
];
```

## Thread Safety
- **HashMap set**: Not thread-safe. HashMap must be owned by current scheduler.
- **Array set**: Not thread-safe. Array must be owned by current scheduler.
- **Shared set**: Not atomic. Use [compareSwap](compareSwap.md) for concurrent updates.

## See Also
- [get](get.md) — retrieve value
- [pushBack](pushBack.md) — append to array
- [compareSwap](compareSwap.md) — atomic CAS for shared
- [createHashMap](createHashMap.md) — create empty hashmap