cargo lipo 
cargo lipo Provides a cargo lipo subcommand which automatically creates a universal library for use with your iOS application.
Note: You still need to have a rustc which can cross-compile to iOS on your path. If cargo fails with error: can't find crate for `std` your rust compiler most likely does not support cross-compiling to iOS.
Note: While cargo lipo can be compiled on stable rust, it requires at least cargo version 0.5.0 to run which currently only ships with the beta.
Until we get a cargo install command you will need to checkout this repository, run cargo build --release and the make sure that target/release/cargo-lipo is somewhere on your $PATH.
From anywhere you would usually run cargo you can now run cargo lipo or cargo lipo --release to create a universal library for ios, which can be found in $target/universal/{release|debug}/$lib_name.a.