rhai/doc/src/rust/modules/create.md

Create a Module from Rust
========================

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


Create via Plugin
-----------------

By far the simplest way to create a [module] is via a [plugin module]
which converts a normal Rust module into a Rhai [module] via procedural macros.


Create via `Module` API
-----------------------

Manually creating a [module] is possible via the `Module` API.

For the complete `Module` API, refer to the [documentation](https://docs.rs/rhai/{{version}}/rhai/struct.Module.html) online.


Use Case 1 – Make the `Module` Globally Available
------------------------------------------------------

`Engine::register_global_module` registers a shared [module] into the _global_ namespace.

All [functions] and [type iterators] can be accessed without _namespace qualifiers_.
Variables and sub-modules are **ignored**.

This is by far the easiest way to expose a module's functionalities to Rhai.

```rust
use rhai::{Engine, Module};

let mut module = Module::new();             // new module

// Use the 'Module::set_fn_XXX' API to add functions.
let hash = module.set_fn_1("inc", |x: i64| Ok(x + 1));

// Remember to update the parameter names/types and return type metadata.
// 'Module::set_fn_XXX' by default does not set function metadata.
module.update_fn_metadata(hash, ["x: i64", "i64"]);

// Register the module into the global namespace of the Engine.
let mut engine = Engine::new();
engine.register_global_module(module.into());

engine.eval::<i64>("inc(41)")? == 42;       // no need to import module
```

Registering a [module] via `Engine::register_global_module` is essentially the _same_
as calling `Engine::register_fn` (or any of the `Engine::register_XXX` API) individually
on each top-level function within that [module].  In fact, the actual implementation of
`Engine::register_fn` etc. simply adds the function to an internal [module]!

```rust
// The above is essentially the same as:
let mut engine = Engine::new();

engine.register_fn("inc", |x: i64| x + 1);

engine.eval::<i64>("inc(41)")? == 42;       // no need to import module
```

Use Case 2 &ndash; Make the `Module` a Static Module
---------------------------------------------------

`Engine::register_static_module` registers a [module] and under a specific module namespace.

```rust
use rhai::{Engine, Module};

let mut module = Module::new();             // new module

// Use the 'Module::set_fn_XXX' API to add functions.
let hash = module.set_fn_1("inc", |x: i64| Ok(x + 1));

// Remember to update the parameter names/types and return type metadata.
// 'Module::set_fn_XXX' by default does not set function metadata.
module.update_fn_metadata(hash, ["x: i64", "i64"]);

// Register the module into the Engine as the static module namespace path
// 'services::calc'
let mut engine = Engine::new();
engine.register_static_module("services::calc", module.into());

// refer to the 'services::calc' module
engine.eval::<i64>("services::calc::inc(41)")? == 42;
```

### Expose Functions to the Global Namespace

The `Module::set_fn_XXX_mut` API methods can optionally expose functions in the [module]
to the _global_ namespace by setting the `namespace` parameter to `FnNamespace::Global`,
so [getters/setters] and [indexers] for [custom types] can work as expected.

[Type iterators], because of their special nature, are _always_ exposed to the _global_ namespace.

```rust
use rhai::{Engine, Module, FnNamespace};

let mut module = Module::new();             // new module

// Expose method 'inc' to the global namespace (default is 'FnNamespace::Internal')
let hash = module.set_fn_1_mut("inc", FnNamespace::Global, |x: &mut i64| Ok(x + 1));

// Remember to update the parameter names/types and return type metadata.
// 'Module::set_fn_XXX_mut' by default does not set function metadata.
module.update_fn_metadata(hash, ["x: &mut i64", "i64"]);

// Register the module into the Engine as a static module namespace 'calc'
let mut engine = Engine::new();
engine.register_static_module("calc", module.into());

// 'inc' works when qualified by the namespace
engine.eval::<i64>("calc::inc(41)")? == 42;

// 'inc' also works without a namespace qualifier
// because it is exposed to the global namespace
engine.eval::<i64>("let x = 41; x.inc()")? == 42;
engine.eval::<i64>("let x = 41; inc(x)")? == 42;
```


Use Case 3 &ndash; Make the `Module` Dynamically Loadable
--------------------------------------------------------

In order to dynamically load a custom module, there must be a [module resolver] which serves
the module when loaded via `import` statements.

The easiest way is to use, for example, the [`StaticModuleResolver`][module resolver] to hold such
a custom module.

```rust
use rhai::{Engine, Scope, Module};
use rhai::module_resolvers::StaticModuleResolver;

let mut module = Module::new();             // new module
module.set_var("answer", 41_i64);           // variable 'answer' under module
module.set_fn_1("inc", |x: i64| Ok(x + 1)); // use the 'set_fn_XXX' API to add functions

// Create the module resolver
let mut resolver = StaticModuleResolver::new();

// Add the module into the module resolver under the name 'question'
// They module can then be accessed via: 'import "question" as q;'
resolver.insert("question", module);

// Set the module resolver into the 'Engine'
let mut engine = Engine::new();
engine.set_module_resolver(resolver);

// Use namespace-qualified variables
engine.eval::<i64>(r#"import "question" as q; q::answer + 1"#)? == 42;

// Call namespace-qualified functions
engine.eval::<i64>(r#"import "question" as q; q::inc(q::answer)"#)? == 42;
```