Marcus Chen
Jan 2026
2 tabs
[features]
default = ["json"]
json = ["serde_json"]
yaml = ["serde_yaml"]
[dependencies]
serde_json = { version = "1", optional = true }
serde_yaml = { version = "0.9", optional = true }
#[cfg(feature = "json")]
pub fn parse_json(input: &str) -> serde_json::Result<serde_json::Value> {
serde_json::from_str(input)
}
2 files · toml, rust
Explain with highlit
Cargo's feature flags let you enable or disable parts of your crate at compile time. I use them for optional dependencies (like serde), platform-specific code, or different build profiles. Features are defined in Cargo.toml and checked with #[cfg(feature = "...")]. The default feature is enabled unless you opt out with --no-default-features. This keeps binary size small and compile times fast by excluding unused code. For libraries, features let users choose their dependencies. For example, a networking crate might have tokio and async-std as separate features. The compiler eliminates disabled code entirely, so there's zero runtime cost. It's a powerful tool for managing complexity in large projects.
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