access-modifiers.md

layout	title	category	tags	order
developer-doc	Access Modifiers	types	types access-modifiers	4

Access Modifiers

While we don't usually like making things private in a programming language, it sometimes the case that it is necessary to indicate that certain fields should not be touched (as this might break invariants and such like). To this end, Enso provides an explicit mechanism for access modification.

• Access Modification
• Private
• Unsafe

Access Modification

Access modifiers in Enso work as follows:

• We have a set of access modifiers, namely private and unsafe.

• We can place these modifiers before a top-level definition.

  type MyAtomType
      type MyAtom a
  
      is_foo : Boolean
      is_foo = ...
  
      private private_method a b = ...
  
      unsafe unsafe_method a b = ...

• By default, accessing any member under an access modifier is an error when performed from another module.

• To use members protected by an access modifier, you must import that access modifier from the file in which you want to access those elements.

  import private Base.Data.Vector
  import unsafe Base.Data.Atom

• These modified imports are available in all scopes, so it is possible to limit the scope in which you have access to the modified definitions.

  function_using_modifiers v x =
      import private Base.Data.Vector
      import unsafe Base.Data.Atom
  
      v.mutate_at_index 0 (_ -> x)
      x = MyAtom.mutate_field name="sum" (with = x -> x + 20)
      x + 20

The actionables for this section are:

• How do we type this?

Private

The private modifier acts to hide implementation details from clients of the API. It is:

• Available by default in the Base library.
• Able to be avoided using the above-described mechanism.

Unsafe

While private works as you might expect, coming from other languages, the unsafe annotation has additional restrictions:

• It must be explicitly imported from Base.Unsafe.
• When you use unsafe, you must write a documentation comment on its usage that contains a section Safety that describes why this usage of unsafe is valid.

The actionables for this section are:

• Specify unsafe properly.