Rust Beta disallows unstable features and building against that is preferred.
src/main.rs:1:1: 1:25 error: unstable feature
src/main.rs:1 #![feature(collections)]
^~~~~~~~~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
src/main.rs:2:1: 2:21 error: unstable feature
src/main.rs:2 #![feature(convert)]
^~~~~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
src/main.rs:3:1: 3:18 error: unstable feature
src/main.rs:3 #![feature(core)]
^~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
src/main.rs:4:1: 4:18 error: unstable feature
src/main.rs:4 #![feature(libc)]
^~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
error: aborting due to 4 previous errors
Could not compile `ykrs`.
Rust Beta disallows unstable features and building against that is preferred.