Visibility and pub

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In Zolo, everything not marked with pub is private to the file where it was declared. Another module that imports the file only sees the public items — functions, constants, structs, enums, traits, and newtypes all follow the same rule.

The support module lib_demo.zolo illustrates this well: greet, add, sub, get_pi, and VERSION are public; internal_helper has no pub and remains invisible from outside:

Only items marked pub appear in the use list. Trying to import internal_helper would cause a compile error.

04-pub-vs-private.zolo

Playground

// Feature: visibility — `pub` exports, no `pub` is private

// Syntax: `pub fn`, `pub const`, `pub struct`, etc. make the

// item visible to other modules. Without `pub`, it is restricted to

// the file.

// When to use: encapsulate internal details, expose only the API.


mod lib_demo

// Only the public API is importable.

use lib_demo::{greet, add, get_pi, VERSION}

fn main() {
  greet("public api")
  print("add(1,2) = {add(1, 2)}")
  print("pi = {get_pi()}")
  print("version = {VERSION}")
  // expected:

  // Hello, public api!

  // add(1,2) = 3

  // pi = 3.14159

  // version = 1.0.0


  // Note: `internal_helper` is in lib_demo.zolo WITHOUT `pub`,

  // so it cannot be imported or called from here.

  // Trying `use lib_demo::internal_helper` or

  // `lib_demo::internal_helper()` is a design error — the

  // function belongs only to the module.

}

The rule is simple: if you want other files to use an item, add pub. If it is an implementation detail, leave it out — the compiler will reject any attempt at external access.

pub const VERSION exports the constant. const VERSION (without pub) would be hidden — even though it is in lib_demo.zolo, no other file could reference it.