# `CEL.Checked`
[🔗](https://github.com/hansihe/pb_ex/blob/v0.2.0/cel_ex/lib/cel/checked.ex#L1)

A type-checked CEL expression, from `CEL.check/2`.

The struct is opaque. Inspect it with:

  * `type/1` and `type/2` — the type of the expression, or of one
    subexpression by id, as a `t:CEL.Type.t/0`.
  * `position/2` — where a subexpression is in the source.
  * `expr/1` — the expression as a tree of `CEL.Expr` nodes.
  * `references/1` — the variable paths it reads and the custom functions it
    calls, with their arguments when they are constants or variable paths.
  * `to_proto/1` — the standard `cel.expr.CheckedExpr` map, for exchange with
    other CEL implementations.

Evaluate it by bundling it with its environment: `CEL.Program.new/2`.

# `arg`

```elixir
@type arg() :: {:const, CEL.Value.t()} | {:var, String.t(), [String.t()]} | :dynamic
```

A call's argument: a constant, a variable path, or anything else.

# `call`

```elixir
@type call() :: %{
  function: String.t(),
  overload_id: String.t(),
  expr_id: expr_id(),
  target: arg() | nil,
  args: [arg()]
}
```

A call to a non-operator function.

# `expr_id`

```elixir
@type expr_id() :: non_neg_integer()
```

The id of a subexpression, as in `CEL.Expr` nodes.

# `position`

```elixir
@type position() :: %{
  offset: non_neg_integer(),
  line: pos_integer(),
  column: pos_integer()
}
```

A place in the source: `offset` counts code points from the start, `line`
and `column` are 1-based and count code points too.

# `references`

```elixir
@type references() :: %{vars: [var_read()], calls: [call()]}
```

What `references/1` returns.

# `t`

```elixir
@type t() :: %CEL.Checked{
  enums: term(),
  expr: term(),
  expr_version: term(),
  ops: term(),
  root_type: term(),
  source_info: term(),
  types: term()
}
```

A type-checked expression; see the module docs.

# `var_read`

```elixir
@type var_read() :: %{name: String.t(), path: [String.t()], expr_id: expr_id()}
```

A variable path an expression reads, such as `req.user.id`.

# `expr`

```elixir
@spec expr(t()) :: CEL.Expr.t()
```

Returns a read-only view of the expression as a tree of `CEL.Expr`
nodes.

# `position`

```elixir
@spec position(t(), expr_id()) :: position() | nil
```

Where the expression with the given id is in the source, or `nil` if the
parser recorded no position for it.

The position is the start of a literal, name, function call or message
literal; the operator of an operator such as `a + b` or `a[0]`; and the
`.` of a field selection or method call. Expressions a macro expands to
share the macro's position.

    checked = CEL.check!("1 +
  x", CEL.Env.build(vars: [x: :int]))
    [_one, x] = CEL.Checked.expr(checked).args

    CEL.Checked.position(checked, x.id)
    #=> %{offset: 6, line: 2, column: 3}

# `references`

```elixir
@spec references(t()) :: references()
```

Returns what the expression reads: variable field paths and non-operator
function calls with their arguments, in evaluation order.

A variable read is the longest field selection rooted at a variable, so
`req.user.id` is one read with path `["user", "id"]`, not three. Variables
a macro binds are resolved to what they stand for: a `cel.bind` or `optMap`
variable to its value, and a comprehension variable to its range followed
by `"*"` for "any element", so `l.exists(i, i.score > 1)` reads `l` and
`l.*.score`. Locals bound to anything other than a variable read are not
reported.

Operators (`_==_`, `@in`, ...), macros and enum constructors are not
reported as calls. A call's `expr_id` is the one a custom function receives
through `eval_context: [:call]`.

# `to_proto`

```elixir
@spec to_proto(t()) :: map()
```

The expression as a standard `cel.expr.CheckedExpr` map (the generated
protobuf shape), for exchange with other CEL implementations.

# `type`

```elixir
@spec type(t()) :: CEL.Type.t()
```

The type of the whole expression.

# `type`

```elixir
@spec type(t(), expr_id()) :: CEL.Type.t() | nil
```

The type of the expression with the given id, or `nil` if the checker did
not type it (such as a comprehension's variable name).

---

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