no such method / unknown method

Why this fires¶

The receiver does not have a method with the given name. Concrete causes:

• A typo (.lenght() instead of .len()).
• The method exists on a different type than the receiver is.
• The method comes from a trait that isn't in scope.
• Visibility — the method is declared but not pub.

let s = "hello"
let n = s.lenght()
//      ^^^^^^^^ error: no method 'lenght' on type 'str'

Fix it¶

1. Fix the spelling¶

Trust the "did you mean?" suggestion when it appears.

2. Bring the trait into scope¶

For methods provided by a trait:

use std::iter::Iterator   // brings `.map`, `.filter`, etc. into scope

3. Check the receiver's actual type¶

The "I'm sure the method exists" case usually means the receiver is a different type than you expect. Add an explicit annotation or hover the value in the editor to confirm:

let parsed: Result<int, ParseError> = input.parse::<int>()
let number: int = parsed.unwrap_or(0)

Strings use text.parse::<int>() or text.parse::<float>() for fallible numeric parsing. There is no string .to_int() or .to_float() method. Concrete string receivers are checked against the standard-library method surface; an Any receiver remains a dynamic boundary.

4. Mark the method pub¶

If you declared the method in an impl block in another module, make sure it's pub.

See also¶

• TE100 — undefined variable (different lookup mechanism).
• /docs/stdlib — built-in methods on str, int, float, etc.