- Comparable.clamp is already defined
- Boolean class does not exist
- String#start_with? already exists
- String#end_with? already exists
- String#bytesize already exists
- String#capitalize already exists
- Integer#digits already exists
- Array#first and Array#last already exist
- Array#shuffle already exists
Ruby's own Integer#digits returns an array with the least significant digit as the first array element. That means that the method's only usage has to be appended with a call to Array#reverse.