missing-accessibility-statement (C131)

This rule is turned on by default.

What it does

Checks for missing private or public accessibility statements in modules

Why is this bad?

The private statement makes all entities (variables, types, procedures) private by default, requiring an explicit public attribute to make them available. As well as improving encapsulation between modules, this also makes it possible to detect unused entities.

A public statement in a module does not change the default behaviour, and therefore all entities will be available from outside the module unless they are individually given a private attribute. This brings all of the same downsides as the default behaviour, but an explicit public statement makes it clear that the programmer is choosing this behaviour intentionally.