How to use Figment with YAML configuration files in Rust?

Figment doesn't support YAML natively. You'll need to implement a custom provider using crates like serde_yaml, or look for third-party providers, though options are limited as per the README's sparse ecosystem.

Figment vs config-rs: which should I use for Rust?

Figment excels at type-safe, concurrency-free merging from multiple sources with a focus on serde integration. config-rs offers more built-in format support and a different API. Choose Figment if race-condition safety and seamless merging are priorities.

Can Figment validate configuration beyond serde deserialization?

No, Figment relies solely on serde for validation. For additional checks, you must implement custom logic after extraction or use serde's features like custom deserializers, which adds complexity.

How to create a custom provider for a database config in Figment?

Implement the Provider trait by defining a data method that returns a Map. Use existing providers like Toml or Env as examples, and ensure your provider integrates with Figment's merging semantics for consistency.

Does Figment support hot-reloading of config files?

No, Figment doesn't support hot-reloading. Configuration is static after extraction. For live updates, you'd need to manually re-extract on changes, which isn't built-in and requires external file watching mechanisms.

What's the performance overhead of using Figment in large apps?

Figment is designed for efficiency with one-time extraction at startup. However, enabling multiple providers via feature flags can increase binary size, and complex merging might add minimal runtime overhead during initialization.

Open-Awesome

Figment

Apache-2.0Rust

A hierarchical configuration library for Rust that merges multiple sources with a concurrency-free design.

GitHub

912 stars51 forks0 contributors

What is Figment?

Figment is a hierarchical configuration library for Rust that allows developers to merge configuration values from multiple sources like TOML files, JSON files, and environment variables into strongly-typed Rust structs. It solves the problem of managing application configuration from diverse sources while maintaining type safety and eliminating concurrency issues.

Target Audience

Rust developers building applications that require configuration from multiple sources, particularly those who need type-safe configuration management without concurrency concerns.

Value Proposition

Developers choose Figment for its concurrency-free design that eliminates race conditions, its seamless integration with serde for type-safe deserialization, and its flexible provider system that supports multiple configuration sources with clear merging semantics.

Overview

A hierarchical configuration library so con-free, it's unreal.

Use Cases

Best For

Managing application configuration from multiple file formats in Rust
Type-safe configuration extraction in Rust applications
Eliminating concurrency issues in configuration access
Merging environment variables with file-based configuration
Building Rust applications with complex configuration requirements
Creating extensible configuration systems with custom providers

Not Ideal For

Projects requiring dynamic, hot-reloadable configuration without application restarts
Applications using YAML or other unsupported formats without custom provider implementation
Simple Rust apps with single-file configuration where plain serde deserialization is sufficient

Pros & Cons

Pros

Hierarchical Merging

Combines configuration from multiple sources like TOML, JSON, and environment variables with clear precedence, as shown in the README example merging 'Cargo.toml', prefixed env vars, and 'Cargo.json'.

Type-Safe Extraction

Uses serde for automatic deserialization into strongly-typed Rust structs, eliminating runtime errors from malformed configuration and ensuring compile-time safety.

Concurrency-Free Design

Eliminates race conditions by design, making configuration access safe in multi-threaded environments without the need for locks or synchronization overhead.

Flexible Environment Integration

Supports prefix-based and raw environment variable selection, allowing fine-grained control over which env vars are included, as demonstrated with 'CARGO_' prefixes and raw keys like 'RUSTC'.

Cons

Limited Built-in Formats

Only supports TOML and JSON out-of-the-box; popular formats like YAML require third-party providers, which are scarce in the ecosystem as noted in the README.

Static Extraction Model

Configuration is extracted once and becomes immutable, with no built-in support for hot-reloading or dynamic updates without re-initializing the extraction process.

Sparse Third-Party Ecosystem

Few external providers are available, limiting extensibility for niche sources or formats, as highlighted by the single listed third-party provider in the README.

Frequently Asked Questions

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