Encapsulation

Introduction

In this page we will explain the use and semantics of the private keyword.

Usage

private works like a headword that modifies other headwords, in that if you write for example:

def

<some functions>

private

<some more functions>

... then the functions below private will be private. The private declaration has scope until the next headword.

Anything you can declare can be declared private: variables, constants, functions, commands, imports, types, and external services (which we haven't met yet). If it has a headword, you can make it private.

Unlike in OO languages, there is no way and no real need to declare individual fields of a struct private.

Semantics

private means, first of all, private from the REPL. An end-user, using Pipefish as its own front-end, can only call public functions and commands, and only see and mutate public variables.

Second, it means private when imported as a library. An application using a Pipefish library is in just the same condition as a human using the same service through its REPL, and is faced with the same API.

Third, it means private when called as an external service. But as we haven't dealt with microservices yet, we'll come back to that.