Private types

[saleynik]

It doesn't seem to be possible to define structs with private types. E.g.:

defstruct [
  a: nil,
  b: nil
]
@typep  t :: %__MODULE__{
  a: integer,
  b: binary
}

It would be great if typedstruct had a visibility or accessor attribute to control private|public visibility.

[ejpcmac]

Indeed, this is a miss. Not sure if there are much use cases for it, since the struct itself cannot be made private, but there is no reason for this feature not to be present.

We already have opaque: true, which we could replace in a later version by visibility: which could be :public (default), :private or :opaque.

[ejpcmac]

This is a design comment

Concept

Let’s add a visibility option to typedstruct that can be :public (default), :private or :opaque.

Requirements

• typedstruct/2 shall accept a visibility option whose values can be :public, :private or :opaque
• The visibility parameter shall be :public when not specified
• visibility: :public shall generate a public type
• visibility: :private shall generate a private type
• visibility: :opaque shall generate an opaque type
• typedstruct/2 shall still accept the opaque option for backward compatibility
• opaque: :true shall have the same effect as visibility: :opaque
• typedstruct/2 shall not accept both visibility and opaque options at the same time
• typedstruct/2 shall emit a deprecation warning when the opaque option is used