No way to get Box<X> out of a Box<X + Y>

[steveklabnik]

Issue by reem
Sunday Nov 02, 2014 at 02:34 GMT

For earlier discussion, see rust-lang/rust#18524

This issue was labelled with: in the Rust repository

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There is currently no way to get a Box<Reader> (or anything else that impls Reader) out of a Box<Reader + Constraint>, for instance Box<Reader + Send>. This is a significant ergonomic problem.

Additionally, Box<Reader + Constraint> should impl Reader since Box<Reader> impls Reader.