NotNilable

A non-null assertion operator for Ruby. Adds Object#not_nil!, ported from TypeScript's ! operator and inspired by Crystal's not_nil!.

When the receiver is anything but nil, .not_nil! returns the receiver unchanged. When it is nil, the method raises NotNilable::NilAssertionError. The bundled RBS signatures let Steep narrow T? to T at the type level.

bundle add not_nilable

require "not_nilable"

"hello".not_nil!   # => "hello"
42.not_nil!        # => 42

nil.not_nil!
# raises NotNilable::NilAssertionError: Nil assertion failed

nil.not_nil!("user must be present")
# raises NotNilable::NilAssertionError: user must be present

With RBS + Steep, the type is narrowed:

val = ENV.fetch("HOME", nil)   # type: String?
val.not_nil!.length            # narrowed to String — .length is OK

After cloning the repo, run bundle install, then bundle exec rake to lint, run specs, and type-check.

MIT.