> For the complete documentation index, see [llms.txt](https://max-daunarovich.gitbook.io/flow-network/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://max-daunarovich.gitbook.io/flow-network/introduction/interfaces/interface-implementation-requirements.md).

# Interface Implementation Requirements

Interfaces can require implementing types to also implement other interfaces of the same kind. Interface implementation requirements can be declared by following the interface name with a colon (`:`) and one or more names of interfaces of the same kind, separated by commas.

```
// Declare a structure interface named `Shape`.
//
pub struct interface Shape {}

// Declare a structure interface named `Polygon`.
// Require implementing types to also implement the structure interface `Shape`.
//
pub struct interface Polygon: Shape {}

// Declare a structure named `Hexagon` that implements the `Polygon` interface.
// This also is required to implement the `Shape` interface,
// because the `Polygon` interface requires it.
//
pub struct Hexagon: Polygon {}
```