A file descriptor can't be -1 but it's not 100% clear whether POSIX bans other negative numbers. So Rust's stdlib only bans -1 (for a space optimization) while still allowing for e.g. -2.
A file descriptor can't be -1 but it's not 100% clear whether POSIX bans other negative numbers. So Rust's stdlib only bans -1 (for a space optimization) while still allowing for e.g. -2.