74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
Export Variables, Functions and Sub-Modules in Module
|
|
===================================================
|
|
|
|
{{#include ../../links.md}}
|
|
|
|
|
|
Export Global Variables
|
|
----------------------
|
|
|
|
The `export` statement, which can only be at global level, exposes selected variables as members 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).
|
|
|
|
```rust
|
|
// 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 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 statement block ends,
|
|
// therefore it is not 'global' and is not exported
|
|
|
|
export inner; // exporting an temporary variable has no effect
|
|
}
|
|
```
|
|
|
|
|
|
Export Functions
|
|
----------------
|
|
|
|
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
|
|
```
|
|
|
|
[`private`] functions are commonly called to initialize the module.
|
|
They cannot be called apart from this.
|
|
|
|
|
|
Sub-Modules
|
|
-----------
|
|
|
|
All loaded modules are automatically exported as sub-modules.
|
|
|
|
To prevent a module from being exported, load it inside a block statement so that it goes away at the
|
|
end of the block.
|
|
|
|
```rust
|
|
// This is a module script.
|
|
|
|
import "hello" as foo; // exported as sub-module 'foo'
|
|
|
|
{
|
|
import "world" as bar; // not exported - the module disappears at the end
|
|
// of the statement block and is not 'global'
|
|
}
|
|
```
|