Slicing discontinuous data into continuous parts in Ruby

I have this discontinuous array:

a = [1, 2, 3, 7, 8, 10, 11, 12]

I need it to be an array of continuous arrays:

[[1, 2, 3], [7, 8], [10, 11, 12]]

method 1:

a = [1, 2, 3, 7, 8, 10, 11, 12]
prev = a[0] - 1
a.slice_before { |cur|  [prev + 1 != cur, prev = cur][0] }.to_a
# => [[1, 2, 3], [7, 8], [10, 11, 12]]

method 2:

a = [1, 2, 3, 7, 8, 10, 11, 12]
prev = a.first
p a.slice_before { |e|
  prev, prev2 = e, prev
  prev2 + 1 != e
}.to_a

method 3:

([a[0]] + a).each_cons(2).slice_before{|k, l| k + 1 != l}.map{|a| a.map(&:last)}