SoFunction
Updated on 2025-04-04

The basics and development process of modular construction of Packages and Crates in Rust

What is Crate?

In Rust, acrateIt is the smallest unit of code considered by the compiler when compiling. Whether throughrustcWhen compiling a separate source file or using Cargo to build the entire project, Rust will treat the input source file as a crate. A crate can contain multiple modules, which can in turn be scattered in different files.

Binary Crate and Library Crate

Crate in Rust is divided into two forms:

  • Binary Crate

Binary crate generates an executable file. Each binary crate must contain a namemainfunction as the entry point of the program. For example, the command line programs we wrote in the previous chapters are all binary crate.

  • Library Crate

Library crate does not containmainFunctions, also do not compile into executable files. They are mainly used to define features that can be shared across multiple projects. For example, commonly usedrandThe library provides the function of generating random numbers. Usually, when Rustaceans mentions "crate", it mostly refers to library crate, which can be conceptually regarded as libraries or modular APIs.

Crate Root

Each crate has onecrate root, that is, the source file that the compiler first looks for when it starts compilation. For binary crate, Cargo will default tosrc/As crate root; for library crate, the default crate root issrc/。

What is Package?

onepackageIt is a collection of codes containing one or more crates. Each package contains oneFile, which describes how to build all crates in package. Simply put, package is the unit used by Cargo to manage and build multiple crates.

For example, when you execute the following command to create a new project:

$ cargo new my-project
     Created binary (application) `my-project` package

At this time, Cargo will generate the following directory structure for you:

my-project/
├── 
└── src
    └──

In this example,defines package, andsrc/It is a binary crate crate root. Note: Cargo will automatically follow the agreementsrc/Considered as a binary crate with the same name as package. If your package is already availablesrc/There is againsrc/, then the package contains both a binary crate and a library crate.

In addition, you can also use thesrc/binPlace extra files in the directory to create multiple binary crates. Each file is compiled into a separate executable, which provides great flexibility for projects that require building multiple tools or command line programs.

The relationship between Package and Crate

  • Package: is a collection of one or more crates, containing oneFiles to describe the project's metadata and build configuration.
  • Crate: is the smallest unit processed by the compiler, divided into binary crate and library crate. Each package contains at least one crate, but can contain multiple binary crates (placesrc/binNext), and can only contain one library crate.

This design makes Rust very flexible when organizing and managing code, allowing you to split functions into independent crates and combine related crates together for unified management through packages.

summary

  • Crateis the smallest unit of code processed by the Rust compiler, which can be binary or library.
  • Crate RootIt is the entry file for each crate, and the default binary crate issrc/, the library crate defaults tosrc/。
  • Packageis a collection of one or more crates, CargoManage the metadata and build configuration of the package.
  • A package can contain multiple binary crates (bysrc/bindirectory), but at most, only one library crate can be included.

Once you have mastered these basic concepts, you will be able to better understand Rust’s module system and manage your projects efficiently with Cargo. Whether building a simple command line tool or developing a huge library project, the correct package and crate structure are the keys to success.

I hope this blog will help you understand the Packages and Crates concepts in Rust more clearly and start your journey of efficient and modular development. Happy coding!

This is the article about Packages and Crates in Rust: the basics of modular construction. For more related Rust Packages and Crates, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!