Germi

Germi is a high-performance, pure Rust environment variable interpolation engine designed for tooling and configuration systems. It allows for safe, deterministic, and flexible variable substitution in strings.

Features

• Pure Rust: Minimal dependencies (only regex is used if enabled, but core is dependency-free).
• High Performance: Designed with zero-copy principles. Returns Cow<'a, str> to avoid allocations when no substitution occurs.
• Comprehensive Syntax:
  • ${VAR} and $VAR
  • Defaults: ${VAR:-default}, ${VAR-default}
  • Conditionals: ${VAR:+val}, ${VAR+val}
  • Escapes: \n, \t, \\, etc.
• Iterative Resolution: Supports nested variable references (VAR="Hello ${USER}").
• Safe: Configurable recursion depth to prevent cycles.

Usage

use germi::Germi;

fn main() {
    let mut germi = Germi::new();
    germi.add_variable("USER", "world");

    let result = germi.interpolate("Hello, ${USER}!").unwrap();
    assert_eq!(result, "Hello, world!");
}

Performance & Tradeoffs

• Scanning: Uses a single-pass scanner that identifies variables and literals.
• Interpolation:
  • Zero-copy fast path: If the input string contains no variables or recursive resolutions, germi returns Cow::Borrowed(input), resulting in zero heap allocations.
  • Allocation on write: Only when a variable is substituted or an escape sequence is processed does germi allocate a new String.
• Recursion: Variable values are recursively resolved. Deep recursion is limited by max_depth (default 10) to prevent stack overflow or infinite loops.

License

MIT