How do you enable a Rust "crate feature"?

Question

I'm trying to use rand::SmallRng. The documentation says

This PRNG is feature-gated: to use, you must enable the crate feature small_rng.

I've been searching and can't figure out how to enable "crate features". The phrase isn't even used anywhere in the Rust docs. This is the best I could come up with:

[features]
default = ["small_rng"]

But I get:

Feature default includes small_rng which is neither a dependency nor another feature

Are the docs wrong, or is there something I'm missing?

kmdreko · Accepted Answer · 2021-09-13 05:36:01Z

83

Specify the dependencies in Cargo.toml like so:

[dependencies]
rand = { version = "0.7.2", features = ["small_rng"] }

Alternatively:

[dependencies.rand]
version = "0.7.2"
features = ["small_rng"]

Both work.

edited Sep 13, 2021 at 5:36

kmdreko

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answered Oct 21, 2019 at 5:27

edwardw

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Comments

dhiraka · Accepted Answer · 2023-07-25 03:04:00Z

25

To add a feature you can use. This works even if you have added the crate initially and want to add a feature later

cargo add rand -F small_rng

edited Jul 25, 2023 at 3:04

answered Jul 24, 2023 at 3:31

dhiraka

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1 Comment

Chayim Friedman Over a year ago

This works even before adding the crate. The -F is a shorthand for --features.

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