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_archive/rhai_engine/rhaibook/language/modules/export.md

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+Export Variables, Functions and Sub-Modules From a Script
+=========================================================
+
+{{#include ../../links.md}}
+
+```admonish info.side "See also"
+
+See [_Create a Module from AST_]({{rootUrl}}/rust/modules/ast.md) for more details.
+```
+
+The easiest way to expose a collection of [functions] as a self-contained [module] is to do it via a Rhai script itself.
+
+The script text is evaluated.
+
+[Variables] are then selectively exposed via the `export` statement.
+
+[Functions] defined by the script are automatically exported, unless marked as `private`.
+
+Modules loaded within this [module] at the global level become _sub-modules_ and are also automatically exported.
+
+
+Export Global Variables
+-----------------------
+
+The `export` statement, which can only be at global level, exposes a selected [variable] as member of a [module].
+
+[Variables] not exported are _private_ and hidden. They are merely used to initialize the [module],
+but cannot be accessed from outside.
+
+Everything exported from a [module] is **[constant]** (i.e. read-only).
+
+```js
+// This is a module script.
+
+let hidden = 123;       // variable not exported - default hidden
+let x = 42;             // this will be exported below
+
+export x;               // the variable 'x' is exported under its own name
+
+export const x = 42;    // convenient short-hand to declare a constant and export it
+                        // under its own name
+
+export let x = 123;     // variables can be exported as well, though it'll still be constant
+
+export x as answer;     // the variable 'x' is exported under the alias 'answer'
+                        // another script can load this module and access 'x' as 'module::answer'
+
+{
+    let inner = 0;      // local variable - it disappears when the statements block ends,
+                        //                  therefore it is not 'global' and cannot be exported
+
+    export inner;       // <- syntax error: cannot export a local variable
+}
+```
+
+```admonish tip.small "Tip: Multiple exports"
+
+[Variables] can be exported under multiple names.
+For example, the following exports three [variables]:
+* `x` as `x` and `hello`
+* `y` as `foo` and `bar`
+* `z` as `z`
+
+~~~js
+export x;
+export x as hello;
+export y as foo;
+export x as world;
+export y as bar;
+export z;
+~~~
+```
+
+
+Export Functions
+----------------
+
+```admonish info.side "Private functions"
+
+`private` [functions] are commonly called within the [module] only.
+They cannot be accessed otherwise.
+```
+
+All [functions] are automatically exported, _unless_ it is explicitly opt-out with the `private` prefix.
+
+[Functions] declared `private` are hidden to the outside.
+
+```rust
+// This is a module script.
+
+fn inc(x) { x + 1 }     // script-defined function - default public
+
+private fn foo() {}     // private function - hidden
+```
+
+
+Sub-Modules
+-----------
+
+All loaded [modules] are automatically exported as sub-modules.
+
+~~~admonish tip.small "Tip: Skip exporting a module"
+
+To prevent a [module] from being exported, load it inside a block statement so that it goes away at the
+end of the block.
+
+```js
+// This is a module script.
+
+import "hello" as foo;      // <- exported
+
+{
+    import "world" as bar;  // <- not exported
+}
+```
+~~~