How to Fix Rangeerror in Rust

Few things halt development faster than an unexpected rangeerror in Rust. The good news is this is a well-understood problem with a clear solution. Let's get you back on track.

What Causes RangeError

A RangeError in Rust occurs when a value falls outside its permitted range. Common triggers include:

• Array or string index out of bounds
• Invalid arguments to built-in functions (negative array sizes, invalid string indices)
• Infinite recursion exceeding the maximum call stack size
• Numeric overflow or underflow in calculations
• Pagination parameters pointing past the end of a collection

How to Fix It

// Rust panics on out-of-bounds indexing — use .get() instead
fn safe_get(data: &[u8], index: usize) -> Option<u8> {
    data.get(index).copied()
}

// For pagination with proper error handling
fn get_page<T>(items: &[T], page: usize, size: usize)
    -> Result<&[T], String>
{
    if size == 0 {
        return Err("Page size must be > 0".into());
    }
    let start = page.saturating_mul(size);
    if start >= items.len() {
        return Ok(&[]);  // Empty page, not an error
    }
    let end = (start + size).min(items.len());
    Ok(&items[start..end])
}

Use .get() instead of direct indexing to avoid panics. Use saturating_mul to prevent overflow on large page numbers.

Prevention Strategies

• Validate all numeric inputs at API boundaries before they reach internal logic
• Add depth limits to recursive algorithms as a safety net
• Use safe accessor methods that return null/None/Option instead of throwing
• Add upper bounds to user-supplied size parameters to prevent resource exhaustion

Catch RangeErrors before they hit production with [Bugsly](https://bugsly.dev) — get full stack traces and the exact value that was out of range for every error in your Rust app.