Using a type with a function or macro that requires a trait the type does not implement.
Rust functions and macros can mandate that types conform to specific interfaces (traits), like `std::fmt::Display` for formatting, `Serialize` for JSON, or `Clone` for duplication.
Attempting to print a custom struct using `println!("{}", my_struct)` without deriving `Display` or `Debug`, or passing a non-comparable type to a sorted data structure.
1struct User {2 name: String,3}4 5fn main() {6 let u = User { name: String::from("Eve") };7 // ERROR E0277: User doesn't implement std::fmt::Display or Debug!8 println!("{:?}", u);9}1// Fix: Add derive macro for Debug and Display implementation2#[derive(Debug)]3struct User {4 name: String,5}6 7fn main() {8 let u = User { name: String::from("Eve") };9 println!("{:?}", u); // Output: User { name: "Eve" }10}Simulate standard system builds to trigger compiler trace records and track memory crashes locally.
The `{:?}` debug formatter requires the type to implement `std::fmt::Debug`. `User` is a plain struct without derive macros, so rustc rejects it.