### Define Project Boundaries

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This example demonstrates how to define module boundaries for a typical Elixir project using the `Boundary` macro. It shows how to specify dependencies between boundaries and which modules are exported.

```elixir
defmodule MySystem do
  use Boundary, deps: [], exports: []
  # ...
end

defmodule MySystemWeb do
  use Boundary, deps: [MySystem], exports: [Endpoint]
  # ...
end

defmodule MySystem.Application do
  use Boundary, top_level?: true, deps: [MySystem, MySystemWeb]
  # ...
end
```

--------------------------------

### Global Configuration for External App Calls

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This example shows how to configure Boundary globally in `mix.exs` to enforce rules on calls to external applications that do not define their own boundaries, such as restricting Phoenix or Ecto usage.

```elixir
defmodule MySystem.MixProject do
  use Mix.Project

  def project do
    [
      # ...
      # Example: Enforce rules for external apps globally
      # boundary: [check_apps: [:phoenix, :ecto]]
      # ...
    ]
  end

  # ...
end
```

--------------------------------

### Configure Boundary Checks in mix.exs

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This snippet shows how to configure Boundary checks within the `mix.exs` file. It specifies which applications and modules Boundary should monitor at compile-time and runtime. In this example, Boundary checks calls to Phoenix, Ecto, and runtime calls to Mix.

```elixir
defmodule MySystem.MixProject do
  def project do
   [
     boundary: [
       default: [
         check: [
           apps: [:phoenix, :ecto, {:mix, :runtime}]
         ]
       ]
     ],
     # ...
   ]
  end
end
```

--------------------------------

### Example of Forbidden Reference Warning

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This Elixir code snippet shows a scenario where a module in `MySystem` attempts to call a function from `MySystemWeb`. The Boundary compiler would detect this as a forbidden reference and emit a warning during compilation.

```elixir
defmodule MySystem.User do
  def auth do
    MySystemWeb.Endpoint.url()
  end
end
```

--------------------------------

### Define Module Boundaries with Boundary

Source: https://github.com/sasa1977/boundary/blob/master/README.md

These examples demonstrate how to use the `use Boundary` macro in Elixir modules to declare dependencies. Each module specifies the external dependencies it is allowed to interact with using the `deps` option. For instance, `MySystemWeb` depends on `Phoenix` and `Ecto.Changeset`, while `MySystem` depends on `Ecto` and `Ecto.Changeset`.

```elixir
defmodule MySystemWeb do
  use Boundary, deps: [Phoenix, Ecto.Changeset]
end

defmodule MySystem do
  use Boundary, deps: [Ecto, Ecto.Changeset]
end

defmodule MySystemMix do
  use Boundary, deps: [Mix]
end
```

--------------------------------

### Integrate Boundary Mix Compiler

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This code snippet illustrates how to include the Boundary compiler in the project's compilation process by adding `:boundary` to the `compilers` list in `mix.exs`.

```elixir
defmodule MySystem.MixProject do
  use Mix.Project

  def project do
    [
      compilers: [:boundary] ++ Mix.compilers(),
      # ...
    ]
  end

  # ...
end
```

--------------------------------

### Add Boundary Dependency in mix.exs

Source: https://github.com/sasa1977/boundary/blob/master/README.md

This snippet shows how to add the Boundary library as a project dependency in the `mix.exs` file. It specifies the version and sets `runtime: false` as Boundary is a compile-time tool.

```elixir
defmodule MySystem.MixProject do
  use Mix.Project

  # ...

  defp deps do
    [
      {:boundary, "~> 0.10", runtime: false},
      # ...
    ]
  end

  # ...
end
```

=== COMPLETE CONTENT === This response contains all available snippets from this library. No additional content exists. Do not make further requests.