# throw

## Category
Error Handling

## Arity
**Unary** — `throw <value>`.

```
throw <any>
```

## Description
Throws an error with the given value. If inside a `try` block, execution jumps to the corresponding `catch` block with the thrown value available as `_exception`. If not inside a `try` block, the fiber terminates with an error.

## How It Works
The compiler emits a throw opcode. The VM unwinds the execution stack to the nearest enclosing `try`/`catch`. If no `try` block is found, the fiber is terminated and the error propagates to the fiber's ScriptHandle.

The caught error is an `SqError` object with properties:
- `.message` — the thrown value as string
- `.file` — source file
- `.line` — line number
- `.col` — column number

## Usage

### Basic throw and catch
```sqf
try {
    if (_hp <= 0) then { throw "Unit is dead"; };
    doWork();
} catch (_error) {
    systemChat f"Error: {_error}";
};
```

### Throw with structured data
```sqf
try {
    if (_index < 0) then { throw ["out_of_range", _index]; };
} catch (_err) {
    _err params ["_code", "_detail"];
    systemChat f"Error {_code}: {_detail}";
};
```

### Validation guard
```sqf
_validatePositive = {
    params ["_val", "_name"];
    if (_val < 0) then {
        throw f"{_name} must be positive, got {_val}";
    };
};

try {
    [_hp, "HP"] call _validatePositive;
    [_armor, "Armor"] call _validatePositive;
} catch (_error) {
    systemChat f"Validation failed: {_error}";
};
```

### Uncaught throw (fiber error)
```sqf
_handle = spawn {
    throw "Something went wrong";
    systemChat "Never reached";
};
// The handle resolves with an error — await will return nil
```

## Thread Safety
Throwing unwinds the current fiber only. Other fibers are unaffected. The `SqError` object is owned by the catching fiber.

## See Also
- [try/catch](try-catch.md) — error handling construct