E0061
Rust Compiler Error
Severity: MinorWhat Does This Error Mean?
Rust E0061 means you called a function with the wrong number of arguments. The error message tells you exactly how many were expected and how many you provided. Count the parameters in the function signature and match your call to it.
Affected Models
- Rust (all stable versions)
Common Causes
- Calling a function with too few arguments
- Calling a function with too many arguments
- Function signature was changed and call sites were not updated
- Calling a macro like a function — macros have different argument rules
- Forgetting that method's self parameter is implicit and not counted in the call
How to Fix It
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Read the error message — it states the expected count and the actual count.
Rust's E0061 message is precise: this function takes 2 arguments but 3 were supplied. Go to the function definition and count its parameters.
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Check the function signature for Option<T> parameters that represent optional values.
Rust has no default function arguments. Optional behaviour is usually handled with Option<T> parameters — you must still pass Some(value) or None explicitly.
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If you changed the function signature, update all call sites.
Rust will show E0061 at every call site that no longer matches the new signature. Use cargo check to find all affected locations quickly.
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Verify you are calling the correct method from the intended trait.
Rust does not support function overloading, but traits can define methods with the same name. Check that you are calling the method from the correct type.
Frequently Asked Questions
Does Rust support default parameter values?
No — Rust does not support default parameter values like Python or C++. The idiomatic alternatives are: use Option<T> for optional parameters, implement the Default trait, or use a builder pattern for structs with many optional fields.
Why is Rust strict about argument counts?
Strict argument counting ensures every function call is explicit and unambiguous. This prevents subtle bugs that arise in languages where missing arguments silently become null or undefined.