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readonly

(★ 267)

Struct fields that are made read-only accessible to other modules

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Download Latest Version (.zip)

- - ci.yml
- FUNDING.yml
- expand.rs
- lib.rs
- - enum.rs
  - enum.stderr
  - readme.rs
  - readme.stderr
  - readonly-meta.rs
  - readonly-meta.stderr
  - unit-struct.rs
  - unit-struct.stderr
- compiletest.rs
- readme.rs
.gitignore
Cargo.toml
LICENSE-APACHE
LICENSE-MIT
README.md

# Installation Guide

1. Get the code

git clone https://github.com/dtolnay/readonly

Downloads the entire project code from GitHub to your computer.

cd readonly

Moves into the project folder you just downloaded.

2. Rust

Medium Recommended

Prerequisites

Git Needed to download the project code from GitHub.
Rust (rustup) Installing via rustup also installs cargo.

cargo build --release

Compiles the Rust project.

cargo run

Builds and then immediately runs the program.

✅ If cargo build finishes without errors, it worked. The executable is created under target/.

// repository documentation

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Readonly
========

[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/readonly-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/readonly)
[<img alt="crates.io" src="https://img.shields.io/crates/v/readonly.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/readonly)
[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-readonly-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/readonly)
[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/readonly/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/readonly/actions?query=branch%3Amaster)

This crate provides an attribute macro to expose struct fields that are readable
and writable from within the same module but readable only outside the module.

```toml
[dependencies]
readonly = "0.2"
```

## Syntax

Place `#[readonly::make]` on a braced struct or tuple struct. This will make all
fields of the struct publicly readable according to their individual visibility
specifiers, but not writable from other modules.

```rust
mod m {
    #[readonly::make]
    pub struct S {
        pub n: i32,
    }

impl S {
        pub fn demo(&mut self) {
            // Can read and write from inside the same module.
            println!("{}", self.n);
            self.n += 1;
        }
    }
}

fn demo(s: &mut m::S) {
    // From outside the module, can only read.
    println!("{}", s.n);

// Does not compile:
    //s.n += 1;
}
```

The error appears as follows.

```console
error[E0594]: cannot assign to data in a dereference of `m::S`
  --> readme.rs:21:5
   |
21 |     s.n += 1;
   |     ^^^^^^^^ cannot assign
```

Optionally, place `#[readonly]` on individual struct fields to make just those
fields publicly readable, without affecting other fields of the struct.

```rust
#[readonly::make]
pub struct S {
    // This field can be read (but not written) by super.
    #[readonly]
    pub(super) readable: i32,

// This field can be neither read nor written by other modules.
    private: i32,
}
```

<br>

#### License

<sup>
Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
</sup>

<br>

<sub>
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.
</sub>