# Register interface
Registering interfaces is similar to registering classes.
First, you have to instantiate the class builder.
[`InterfaceEntity`](phper::classes::InterfaceEntity),
then extends interfaces (if there are),
add public abstract methods, finally add it into the `Module`.
Here is the simplest example:
```rust,no_run
use phper::{classes::InterfaceEntity, modules::Module, php_get_module};
#[php_get_module]
pub fn get_module() -> Module {
let mut module = Module::new(
env!("CARGO_CRATE_NAME"),
env!("CARGO_PKG_VERSION"),
env!("CARGO_PKG_AUTHORS"),
);
let foo = InterfaceEntity::new("Foo");
module.add_interface(foo);
module
}
```
Similarly in PHP:
```php
<?php
interface Foo {}
```
## Extends interfaces
If you want the interface `Foo` extends `ArrayAccess` and `Iterator` interfaces.
```rust,no_run
use phper::classes::{Interface, InterfaceEntity, ClassEntry};
let mut foo = InterfaceEntity::new("Foo");
foo.extends(Interface::from_name("ArrayAccess"));
foo.extends(Interface::from_name("Iterator"));
```
Same as:
```php
<?php
interface Foo extends ArrayAccess, Iterator {}
```
## Add methods
Interface can add public abstract methods, and public static abstract methods.
```rust,no_run
use phper::classes::{InterfaceEntity, ClassEntry, Visibility};
use phper::functions::Argument;
use phper::objects::StateObj;
use phper::values::ZVal;
let mut foo = InterfaceEntity::new("Foo");
foo.add_method("doSomethings").argument(Argument::new("name"));
foo.add_static_method("test");
```
Note that abstract has no method body, so you don't need to add the handler to the method.
## Add constants
Interfaces can have public constants. Value can be string|int|bool|float|null.
```rust,no_run
use phper::classes::InterfaceEntity;
let mut foo = InterfaceEntity::new("Foo");
foo.add_constant("ONE", "one");
foo.add_constant("TWO", 2);
foo.add_constant("THREE", 3.0);
```