Forty Six and Two: Accessibility modifiers on F# record types

26 May 2012

Accessibility modifiers on F# record types

In the note to self category.

type internal Internal = { Si : string }

means that the class Internal will be internal. The constructor and properties are technically public, but that is meaningless since the enclosing class is internal. However, if the Internal type implements public interfaces, then the public methods it implements are visible and usable by clients outside the assembly (provided they get hold of an instance, of course – they can’t construct one since they can’t see the name of the class).

type IGet = abstract Get : string

type internal Internal = 
    { Si : string }
    interface IGet with
        member x.Get = x.Si

If an instance gets out as an obj, clients can still call HashCode and Equals because those are exposed as public overrides from obj or as public interfaces, e.g. IComparable.

type Internal = internal { Si : string }

means that the class Internal is public, but the constructor and properties are internal.

Both can be combined, and private of course works too. Similar accessibility modifiers can be given to discriminated unions – it is not possible to give a different accessibility to individual union cases, just like it isn’t possible to give different modifiers to different fields of a record.