cpp-like lower_bound, upper_bound in Ruby

bound.rb

def lowerBound(a, key)
    lb = -1; ub = a.length
    while ub - lb > 1
        mid = (lb + ub) / 2
        if a[mid] >= key
            ub = mid
        else
            lb = mid
        end
    end
    ub
end
def upperBound(a, key)
    lb = -1; ub = a.length
    while ub - lb > 1
        mid = (lb + ub) / 2
        if a[mid] <= key
            lb = mid
        else
            ub = mid
        end
    end
    ub
end

bound_bsearch.rb

def lowerBound(a, key)
    idx = (0...a.size).bsearch { |i| a[i] >= key }
    #idx = bsearch_index { |e| e >= key } #Ruby 2.3 and later
    idx.nil? ? a.size : idx
end
def upperBound(a, key)
    idx = (0...a.size).bsearch { |i| a[i] > key }
    #idx = bsearch_index { |e| e > key } #Ruby 2.3 and later
    idx.nil? ? a.size : idx
end