# `cargo rustc` for passing arbitrary flags to rustc

`cargo rustc` is a new subcommand for Cargo that allows you to pass arbitrary `rustc` flags through Cargo.

For example, Cargo does not have a way to pass unstable flags built-in. But if we'd like to use `print-type-sizes` to see what layout information our types have, we can run this:

    $ cargo rustc -- -Z print-type-sizes

And we'll get a bunch of output describing the size of our types.

## Note

`cargo rustc` only passes these flags to invocations of your crate, and not to any `rustc` invocations used to build dependencies. If you'd like to do that, see `$RUSTFLAGS`.