Predicator.Undefined (predicator v3.7.0)

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The :undefined sentinel: predicator's representation of an unbound or missing value.

The atom stays the runtime representation - it is pervasive in tests and the Ruby/JavaScript siblings, JSON-adjacent, and cheap. A struct sentinel would break instruction interchange and every existing embedding for aesthetic gain (the instruction list is the cross-language interchange format, ADR-0001). This module owns it publicly instead: one place that names the atom, checks for it, and normalizes it against nil at a JSON-shaped boundary.

Summary

Functions

from_nil(value)

Converts nil to the :undefined sentinel; any other value passes through unchanged. The inverse of to_nil/1.

to_nil(value)

Converts the :undefined sentinel to nil; any other value passes through unchanged.

undefined?(arg1)

Checks whether value is the :undefined sentinel.

value()

The :undefined sentinel value.

Functions

from_nil(value)

@spec from_nil(Predicator.Types.value() | nil) :: Predicator.Types.value()

Converts nil to the :undefined sentinel; any other value passes through unchanged. The inverse of to_nil/1.

For normalizing an incoming nil (JSON null, a host application's own "missing") to predicator's sentinel at the edge.

Examples

iex> Predicator.Undefined.from_nil(nil)
:undefined

iex> Predicator.Undefined.from_nil(42)
42

to_nil(value)

@spec to_nil(Predicator.Types.value()) :: Predicator.Types.value() | nil

Converts the :undefined sentinel to nil; any other value passes through unchanged.

For embedding at a boundary that speaks nil rather than :undefined (JSON output, a host application's own representation of "missing").

Examples

iex> Predicator.Undefined.to_nil(:undefined)
nil

iex> Predicator.Undefined.to_nil(42)
42

undefined?(arg1)

@spec undefined?(Predicator.Types.value() | nil) :: boolean()

Checks whether value is the :undefined sentinel.

Examples

iex> Predicator.Undefined.undefined?(:undefined)
true

iex> Predicator.Undefined.undefined?(nil)
false

iex> Predicator.Undefined.undefined?(42)
false

value()

@spec value() :: :undefined

The :undefined sentinel value.

Examples

iex> Predicator.Undefined.value()
:undefined