rhai/doc/src/safety/max-map-size.md

Maximum Size of Object Maps
==========================

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Limit How Large Object Maps Can Grow
-----------------------------------

Rhai by default does not limit how large (i.e. the number of properties) an [object map] can be.

This can be changed via the `Engine::set_max_map_size` method, with zero being unlimited (the default).

A script attempting to create an object map literal with more properties than the maximum will terminate with a parse error.

Any script operation that produces an object map with more properties than the maximum also terminates the script with an error result.

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

```rust
let mut engine = Engine::new();

engine.set_max_map_size(500);   // allow object maps with only up to 500 properties

engine.set_max_map_size(0);     // allow unlimited object maps
```


Setting Maximum Size
-------------------

Be conservative when setting a maximum limit and always consider the fact that a registered function may grow
an object map's size without Rhai noticing until the very end.

For instance, the built-in '`+`' operator for object maps concatenates two object maps together to form one larger object map;
if both object maps are _slightly_ below the maximum size limit, the resultant object map may be almost _twice_ the maximum size.

As a malicious script may create a deeply-nested object map which consumes huge amounts of memory while each individual
object map still stays under the maximum size limit, Rhai also recursively adds up the sizes of all [strings], [arrays]
and [object maps] contained within each object map to make sure that the _aggregate_ sizes of none of these data structures
exceed their respective maximum size limits (if any).