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

Native adapters for protobuf well-known types.

`projections/1` returns ready-to-use entries for the `:projections` option of
`PB.compile/2` and `PB.Schema`. The adapters are opt-in — nothing is applied
to a schema that does not register them.

    PB.compile(descriptor_set,
      projections: PB.WellKnownTypes.projections([:time, :wrappers, :json])
    )

## Representations

Each group maps a set of well-known messages to a native Elixir value:

### `:time`

  * `google.protobuf.Timestamp` → `{:timestamp, unix_nanoseconds}`
  * `google.protobuf.Duration` → `{:duration, nanoseconds}`

Integer nanoseconds keep protobuf precision intact. Higher-level
integrations can expose lossy `DateTime` / `Duration` forms explicitly via a
custom `PB.Adapter`.

### `:wrappers`

The scalar wrapper messages unwrap to their bare scalar value (or `nil` when
absent):

  * `google.protobuf.{Int32,Int64,UInt32,UInt64}Value` → `integer`
  * `google.protobuf.{Float,Double}Value` → `float`
  * `google.protobuf.BoolValue` → `boolean`
  * `google.protobuf.StringValue` → `String.t()`
  * `google.protobuf.BytesValue` → `binary`

### `:json`

The JSON-value messages map to JSON-shaped Elixir terms:

  * `google.protobuf.Value` → `nil | boolean | number | String.t() | list | map`
  * `google.protobuf.ListValue` → `list`
  * `google.protobuf.Struct` → `map` with string keys

See [Adapters and well-known types](adapters-and-well-known-types.html) for
how adapters compose with encode, decode, JSON, and validation.

# `duration`

```elixir
@type duration() :: {:duration, integer()}
```

Native representation of `google.protobuf.Duration` (`:time` group).

# `group`

```elixir
@type group() :: :wrappers | :json | :time
```

# `timestamp`

```elixir
@type timestamp() :: {:timestamp, integer()}
```

Native representation of `google.protobuf.Timestamp` (`:time` group).

# `projections`

```elixir
@spec projections(group() | [group()]) :: [{PB.message_name(), keyword()}]
```

Returns PB projection entries for a well-known type group or list of
groups.

---

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