rhaj/rhai_engine/rhaibook/safety/max-variables.md

Maximum Number of Variables

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Rhai by default does not limit how many [variables]/[constants] can be defined within a single [Scope].

This can be changed via the [Engine::set_max_variables][options] method. Notice that setting the maximum number of [variables] to zero does not indicate unlimited [variables], but disallows defining any [variable] altogether.

A script attempting to define more than the maximum number of [variables]/[constants] will terminate with an error result.

This check can be disabled via the [unchecked] feature for higher performance (but higher risks as well).

let mut engine = Engine::new();

engine.set_max_variables(5);      // allow defining only up to 5 variables

engine.set_max_variables(0);      // disallow defining any variable (maximum = zero)

engine.set_max_variables(1000);   // set to a large number for effectively unlimited variables

Each [function] call creates a new, empty [`Scope`].

Therefore, [variables]/[constants] defined within [functions] are counted afresh.

Care must be taken to avoid deeply-nested (or recursive) [function] calls from creating too many
[variables]/[constants] while staying within the limit of each individual [`Scope`].

The parameters of a [function] also count as [variables] within the [function]'s [`Scope`].

Thus the maximum number of [variables]/[constants] allowed is reduced by the number of parameters of the [function].

It is possible to _reuse_ a [variable] such that it is counted only once.

```rust
let x = 42;     // counted as 1 variable
let y = 123;

let x = 0;      // previous 'x' reused: not counted as new variable
```