Script Optimization
===================

{{#title Script Optimization}}

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Rhai includes an _optimizer_ that tries to optimize a script after parsing.
This can reduce resource utilization and increase execution speed.

Script optimization can be turned off via the [`no_optimize`] feature.


Optimization Levels
===================

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There are three levels of optimization: `None`, `Simple` and `Full`.
The default is `Simple`.

An [`Engine`]'s optimization level is set via [`Engine::set_optimization_level`][options].

```rust
// Turn on aggressive optimizations
engine.set_optimization_level(rhai::OptimizationLevel::Full);
```

`None`
------

`None` is obvious – no optimization on the AST is performed.


`Simple` (Default)
------------------

`Simple` performs only relatively _safe_ optimizations without causing side-effects (i.e. it only
relies on static analysis and [built-in operators] for [constant] [standard types], and will not
perform any external function calls).

```admonish warning.small
After _constants propagation_ is performed, if the [constants] are then modified (yes, it is possible, via Rust functions),
the modified values will _not_ show up in the optimized script.

Only the initialization values of [constants] are ever retained.
```

```admonish warning.small

Overriding a [built-in operator] in the [`Engine`] afterwards has no effect after the
optimizer replaces an expression with its calculated value.
```

`Full`
------

`Full` is _much_ more aggressive, _including_ calling external functions on [constant] arguments to
determine their results.

One benefit to this is that many more optimization opportunities arise, especially with regards to
comparison operators.