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# Error code E0225

Multiple types were used as bounds for a closure or trait object.

Erroneous code example:

    fn main() {
        let _: Box<dyn std::io::Read + std::io::Write>;
    }

Rust does not currently support this.

Auto traits such as Send and Sync are an exception to this rule: It's possible to have bounds of one non-builtin trait, plus any number of auto traits. For example, the following compiles correctly:

    fn main() {
        let _: Box<dyn std::io::Read + Send + Sync>;
    }