Ruby on Rails - ActiveSupport: Array Extensions

Question

In the extensions to the array class (rails/activesupport/lib/active_support/core_ext/array/access.rb) the following function is defined:

# Returns the beginning of the array up to +position+.
def to(position)
  if position >= 0
    take position + 1
  else
    self[0..position]
  end
end

Why is it defined like this? Why can't we just do:

def to(position)
  self[0..position]
end

Answer 1

According to the commit message of the change in the Rails code , it looks like they were trying to "Avoid creating range objects".

When I do arr[0..3] , the 0..3 part becomes a Range object, which then gets used to calculate the subarray. I'm guessing they were trying to save memory by avoiding this.

Answer 2

It's about efficiency. Since most use case (positive parameter) will fall into the if branch and the Array#take method easily gives the return, see implementation:

               static VALUE
rb_ary_take(VALUE obj, VALUE n)
{
    long len = NUM2LONG(n);
    if (len < 0) {
        # does not take negative parameter
        rb_raise(rb_eArgError, "attempt to take negative size");
    }
    return rb_ary_subseq(obj, 0, len);
}

For the else branch, we have to create a rang object since Array#take does not take a negative parameter (see above c implementation) and hence a little more memory is used.