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Asked: 2026-06-03T20:00:58+00:00

From examining the documentation for Ruby 1.9.3, both Array#<< and Array#push were designed to

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From examining the documentation for Ruby 1.9.3, both Array#<< and Array#push were designed to implement appending an element to the end of the current array. However, there seem to be subtle differences between the two.

The one I have encountered is that the * operator can be used to append the contents of an entire other array to the current one, but only with #push.

a = [1,2,3]
b = [4,5,6]

a.push *b
=> [1,2,3,4,5,6]

Attempting to use #<< instead gives various errors, depending on whether it’s used with the dot operator and/or parentheses.

Why does #<< not work the same way #push does? Is one not actually an alias for the other?

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1 Answer

  1. Editorial Team

    They are very similar, but not identical.

    << accepts a single argument, and pushes it onto the end of the array.

    push, on the other hand, accepts one or more arguments, pushing them all onto the end.

    The fact that << only accepts a single object is why you’re seeing the error.

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