Practical Crates

Feature Toggle

Select an Output Shape

Crates often expose feature flags that choose one behavior while keeping the public call site small.

Program

Play the program to choose a JSON-shaped output or a compact text output.

feature_toggle.rs 
fn main() {
    let json_output = ;
    let summary = build_summary("search", 3, json_output);
    println!("{summary}");
}

fn build_summary(name: &str, count: i32, json_output: bool) -> String {
    if json_output {
        format!("{{\"name\":\"{name}\",\"count\":{count}}}")
    } else {
        format!("{name}:{count}")
    }
}

fn main() {
    let json_output = ;
    let summary = build_summary("search", 3, json_output);
    println!("{summary}");
}

fn build_summary(name: &str, count: i32, json_output: bool) -> String {
    if json_output {
        format!("{{\"name\":\"{name}\",\"count\":{count}}}")
    } else {
        format!("{name}:{count}")
    }
}
feature flag `json_output` stands in for a crate feature that selects one output strategy.
branch Only one formatting branch runs for a chosen feature shape.
API boundary `build_summary` hides the formatting choice behind one small function.