envy
A Rust library for deserializing environment variables into type-safe structs using Serde.
What is envy?
Envy is a Rust crate that simplifies configuration management by automatically deserializing environment variables into strongly-typed Rust structs. It leverages Serde's deserialization framework to provide a safe and ergonomic way to handle application configuration from the environment, preventing runtime errors through compile-time type checking.
Rust developers building applications that require configuration via environment variables, particularly those using the Serde ecosystem for serialization and deserialization.
Developers choose Envy for its seamless integration with Serde, offering type safety and flexibility with features like optional fields, vector support, and prefixed variables, all while adhering to Rust's philosophy of safety and explicitness.
Overview
deserialize env vars into typesafe structs with rust
Use Cases
Best For
- Deserializing environment variables into type-safe Rust structs with compile-time validation.
- Managing application configuration in Rust projects that use Serde for serialization.
- Handling optional configuration fields where environment variables may be absent.
- Parsing comma-separated environment variable values into Vec types.
- Namespacing environment variables with custom prefixes to avoid naming conflicts in multi-service applications.
- Setting sensible default values for configuration fields when environment variables are not provided.
Not Ideal For
- Applications requiring dynamic configuration reloading without restarting, as Envy only deserializes at startup.
- Projects that prefer configuration via TOML or JSON files without environment variable management overhead.
- Teams already using comprehensive configuration crates like config-rs that support multiple sources and formats.
Pros & Cons
Pros
Envy deserializes environment variables into Rust structs with compile-time validation, preventing runtime errors as shown in examples where mismatched types cause deserialization failures.
Built on Serde, it supports all Serde attributes for custom deserialization, such as using #[serde(default="function")] to specify defaults, enhancing flexibility.
Automatically manages missing env vars for Option types and parses comma-separated values into Vec, simplifying common configuration patterns without extra code.
Provides envy::prefixed(prefix) to namespace env vars, avoiding conflicts in multi-service apps as demonstrated with the APP_ prefix example.
Cons
Only deserializes from environment variables, so projects needing mixed sources like files or command-line arguments must integrate additional crates.
Configuration is loaded once at startup; Envy doesn't support hot-reloading of environment variables without manual reinitialization or external tools.
Heavy reliance on Serde adds compile-time complexity and requires familiarity with Serde's attributes for advanced customization, which can be a barrier.
Frequently Asked Questions
Related Projects
config-rs⚙️ Layered configuration system for Rust applications (with strong support for 12-factor applications).
FigmentA hierarchical configuration library so con-free, it's unreal.
configure_meA Rust library for processing application configuration easily
cfg-rsA Configuration Library for Rust Applications
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