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48 lines
1.9 KiB
Markdown
48 lines
1.9 KiB
Markdown
# Prefer small crates
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## Description
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Prefer small crates that do one thing well.
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Cargo and crates.io make it easy to add third-party libraries, much more so than
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in say C or C++. Moreover, since packages on crates.io cannot be edited or
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removed after publication, any build that works now should continue to work in
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the future. We should take advantage of this tooling, and use smaller, more
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fine-grained dependencies.
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## Advantages
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- Small crates are easier to understand, and encourage more modular code.
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- Crates allow for re-using code between projects. For example, the `url` crate
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was developed as part of the Servo browser engine, but has since found wide
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use outside the project.
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- Since the compilation unit of Rust is the crate, splitting a project into
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multiple crates can allow more of the code to be built in parallel.
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## Disadvantages
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- This can lead to "dependency hell", when a project depends on multiple
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conflicting versions of a crate at the same time. For example, the `url` crate
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has both versions 1.0 and 0.5. Since the `Url` from `url:1.0` and the `Url`
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from `url:0.5` are different types, an HTTP client that uses `url:0.5` would
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not accept `Url` values from a web scraper that uses `url:1.0`.
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- Packages on crates.io are not curated. A crate may be poorly written, have
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unhelpful documentation, or be outright malicious.
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- Two small crates may be less optimized than one large one, since the compiler
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does not perform link-time optimization (LTO) by default.
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## Examples
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The [`url`](https://crates.io/crates/url) crate provides tools for working with
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URLs.
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The [`num_cpus`](https://crates.io/crates/num_cpus) crate provides a function to
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query the number of CPUs on a machine.
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The [`ref_slice`](https://crates.io/crates/ref_slice) crate provides functions
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for converting `&T` to `&[T]`. (Historical example)
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## See also
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- [crates.io: The Rust community crate host](https://crates.io/)
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