E0369: binary operation cannot be applied to type Rust Origin: Application & API OSI layer 7 · Application Last updated 5 Nov 2026

Rust: error[E0369]: binary operation `+` cannot be applied to type `Foo` / cannot add `&str` to `&str`

An operator (+, ==, <) isn't implemented for the operand types.

Exact message you may see error[E0369]: binary operation `+` cannot be applied to type `&str`cannot add `&str` to `&str`error[E0369]: binary operation `==` cannot be applied to type `Foo`binary operation `+` cannot be applied to type `T`error[E0369]: binary operation `<` cannot be applied
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Seen on: Rust

Meaning

Implement the operator trait (impl Add for Foo, #[derive(PartialEq)] for ==), convert types (String + &str, format!), or dereference references. &str + &str isn't allowed: use format!("{a}{b}") or a.to_owned() + b. Floats don't implement Eq/Ord.

Common causes

  • &str + &str
  • Custom struct without Add/PartialEq impl
  • References vs values (&i32 + i32 is ok, &Foo + Foo not)
  • Comparing floats with Ord
  • Generic T lacking the operator bound

⚡ Quick fix

  1. format!("{a}{b}") or a.to_string() + b
  2. #[derive(PartialEq)] / impl Add for Foo
  3. Add bounds T: std::ops::Add<Output = T>

Detailed fix by platform

Rust

  1. let s = format!("{first} {last}");

How to diagnose

  1. Operator — Trait implemented?
  2. Types — Reference/owned?
  3. Bound — Generic?

🔧 Still not fixed?

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Where this error sits

Origin: Application & API. Errors that are often confused with or caused by this one (click to open):

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