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access-modifiers.md

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Access Modifiers

[!WARNING] Everybody who ever maintained a large system knows encapsulation is essential.

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.

Enso targets large user base of non-programmers. They are mostly focused on getting their job done and encapsulation of their own code is the last thing that comes to their mind.

On the other hand, Enso supports and encourages creation of sharable libraries. Maintainers of such libraries are likely to treat API design and its backward compatibility seriously. As such they need a way to encapsulate internals of their libraries and clearly differentiate public API and implementations details.

Access Modification

By default Enso elements (functions, types, methods) are public. One has to use an access modifier to hide and encapsulate them. The reasoning is: those who don't care can access everything they create without any restriction. Those who care can make things private with an additional effort.

Accessing any member under an access modifier is an error when performed from another project. Such a check is enforced during runtime.

There is a command line switch to disable access modifier check. It maybe be useful for experimentation. However the general suggestion is: Avoid using it in production.

Private

Encapsulation is an effective communication mechanism among distributed groups of developers. The private modifier hides implementation details from clients of the API. The primary groups in the Enso case are those who publish a library and those who consume such a library.

As such Enso supports library private encapsulation. To hide any element (module, type, constructor, function) away from library consumers prefix such an element with private keyword.