# `PB.CEL`
[🔗](https://github.com/hansihe/pb_ex/blob/v0.2.0/pb_cel/lib/pb/cel.ex#L1)

CEL expressions over protobuf messages: `types/1` makes a PB schema's
messages and enums the types of a `CEL.Env`.

    env =
      CEL.Env.build(
        types: PB.CEL.types(MyApp.Schema),
        container: "my.pkg",
        vars: [user: {:message, "my.pkg.User"}]
      )

    CEL.eval("user.age >= 18 && user.role == Role.ADMIN", %{user: user}, env)

Message and enum types are named by PB's atoms, so a message value is
`{:message, :"my.pkg.User", fields}` and an enum value
`{:enum, :"my.pkg.Role", 2}`. A message variable binds to the message as
`PB.decode/4` returns it, and an enum variable to a value's name as an
atom or its number. The well-known types are the CEL types they stand for:
a `google.protobuf.Timestamp` field reads as a timestamp, an
`Int64Value` one as an int or `null`.

# `types`

```elixir
@spec types(PB.schema() | module()) :: CEL.TypeProvider.t()
```

The `CEL.TypeProvider` for `schema`: a module that `use PB.Schema`, or a
compiled schema from `PB.compile/2`.

A module is kept as it is and its schema read when needed, so environments
and programs stay small.

---

*Consult [api-reference.md](api-reference.md) for complete listing*