What is the difference between #concat and += on Arrays?

Question

I want to concatenate two Arrays in Ruby. So far I have found the #concat and the += operator. They seem to produce the same result, but I want to know what is the difference between them.

• Where can I find the documentation for the += operator?
• What are the differences between #concat and using the += operator on Arrays?

Answer 1

+= would create a new array object, concat mutates the original object

a = [1,2]
a.object_id # => 19388760 
a += [1]
a.object_id # => 18971360 


b = [1,2]
b.object_id # => 18937180 
b.concat [1]
b.object_id # => 18937180 

Note the object_id for a changed while for b did not change