Rust Code Simplifier

Proactive pattern guide for writing simple, idiomatic Rust. Apply these patterns whenever writing or modifying Rust code — not only when asked to simplify.

Project rules: These patterns align with .claude/rules/rust-patterns.md. When in doubt, re-read the rules file.

1. Iterator Chains Over Manual Loops

Use iterator chains for transformation logic. Reserve for loops only when the body needs early error returns with ?.

// WRONG
let mut names = Vec::new();
for tool in tools {
    if tool.is_available() {
        names.push(tool.name().to_owned());
    }
}

// RIGHT
let names: Vec<String> = tools
    .iter()
    .filter(|t| t.is_available())
    .map(|t| t.name().to_owned())
    .collect();

When to keep a loop: The body calls fallible operations with ?:

// Loop is correct here — early return on error
for entry in entries {
    let meta = entry.metadata().context("failed to read metadata")?;
    process(&meta).await?;
}

2. Option/Result Chaining

Flatten nested match/if let on Option/Result into chained combinators or ?.

// WRONG — nested match pyramid
match config.project.as_ref() {
    Some(project) => match project.settings.as_ref() {
        Some(settings) => match settings.get("key") {
            Some(val) => Some(val.to_owned()),
            None => None,
        },
        None => None,
    },
    None => None,
}

// RIGHT — ? operator for Option propagation
config
    .project
    .as_ref()?
    .settings
    .as_ref()?
    .get("key")
    .map(|v| v.to_owned())

Combinator quick reference:

3. Early Returns

Guard against invalid/empty states at the top. Avoid deep nesting for the main logic.

// WRONG — main logic buried in nested conditions
fn process(entries: &[Entry], prefix: &str) -> Vec<String> {
    let mut results = Vec::new();
    if !entries.is_empty() {
        if !prefix.is_empty() {
            for entry in entries {
                if entry.name.starts_with(prefix) {
                    results.push(entry.name.strip_prefix(prefix).unwrap().to_owned());
                }
            }
        }
    }
    results
}

// RIGHT — guard clauses, then flat logic
fn process(entries: &[Entry], prefix: &str) -> Vec<String> {
    if entries.is_empty() || prefix.is_empty() {
        return Vec::new();
    }

    entries
        .iter()
        .filter(|e| e.name.starts_with(prefix))
        .filter_map(|e| e.name.strip_prefix(prefix))
        .map(|s| s.to_owned())
        .collect()
}

Signals to look for: is_empty(), is_none(), is_err(), boolean flags checked before the real work begins.

4. Avoid Redundant Clones

Borrow instead of cloning. When ownership is needed, use .to_owned() (not .clone()). Use String::from("...") for string literals (not "...".to_string()).

// WRONG — clones where borrows suffice
fn format_tool(tool: &Tool) -> String {
    let data = tool.data.clone();
    let name = tool.name.clone();
    format!("{}: {}", name, data)
}

// RIGHT — format! borrows automatically
fn format_tool(tool: &Tool) -> String {
    format!("{}: {}", tool.name, tool.data)
}

// WRONG
let label = "default".to_string();
let copy = config.clone();

// RIGHT
let label = String::from("default");
let copy = config.to_owned();

5. if let for Single-Variant Match

Use match only when both arms carry logic. Use if let when only one variant matters.

// WRONG — match with throwaway arm
match result {
    Some(val) => process(val),
    None => (),
}

// RIGHT
if let Some(val) = result {
    process(val);
}

// RIGHT — match when both arms carry logic
match result {
    Ok(ctx) => tool.format(ctx).await,
    Err(e) => log_and_report(e),
}

Common Mistakes