rhaj/rhai_engine/rhaibook/safety/checked.md

Turning Off Safety Checks
=========================

{{#include ../links.md}}


Checked Arithmetic
------------------

```admonish bug.side "Don't Panic"

Scripts under normal builds of Rhai never crash the host system – any panic is a bug.
```

By default, all arithmetic calculations in Rhai are _checked_, meaning that the script terminates
with a runtime error whenever it detects a numeric over-flow/under-flow condition or an invalid
floating-point operation.

This checking can be turned off via the [`unchecked`] feature for higher performance (but higher
risks as well).

```rust
let x = 1_000_000_000_000;

x * x;      // Normal build - runtime error: multiplication overflow

x * x;      // 'unchecked' debug build - panic!
            // 'unchecked' release build - overflow with no error

x / 0;      // Normal build - runtime error: division by zero

x / 0;      // 'unchecked' build - panic!
```


Other Safety Checks
-------------------

In addition to overflows, there are many other safety checks performed by Rhai at runtime.
[`unchecked`] turns them **all** off as well, such as...

### [Infinite loops][maximum number of operations]

```rust
// Normal build - runtime error: exceeds maximum number of operations
loop {
    foo();
}

// 'unchecked' build - never terminates!
loop {
    foo();
}
```

### [Infinite recursion][maximum call stack depth]

```rust
fn foo() {
    foo();
}

foo();      // Normal build - runtime error: exceeds maximum stack depth

foo();      // 'unchecked' build - panic due to stack overflow!
```

### [Gigantic data structures][maximum size of arrays]

```rust
let x = [];

// Normal build - runtime error: array exceeds maximum size
loop {
    x += 42;
}

// 'unchecked' build - panic due to out-of-memory!
loop {
    x += 42;
}
```

### Improper range iteration

```rust
// Normal build - runtime error: zero step
for x in range(0, 10, 0) { ... }

// 'unchecked' build - never terminates!
for x in range(0, 10, 0) { ... }

// Normal build - empty range
for x in range(0, 10, -1) { ... }

// 'unchecked' build - panic due to numeric underflow!
for x in range(0, 10, -1) { ... }
```