What's the difference between these two statements? I use them in my rails app and to me it looks like they do the same thing
array_a = Array.new
array_b = []
5 Answers
Those two statements are functionally identical. Array.new however can take arguments and a block:
Array.new # => []
Array.new(2) # => [nil,nil]
Array.new(5,"A") # =>["A","A","A","A","A"]
a = Array.new(2,Hash.new)
a[0]['cat'] = 'feline'
a # => [{"cat"=>"feline"},{"cat"=>"feline"}]
a[1]['cat'] = 'Felix'
a # => [{"cat"=>"Felix"},{"cat"=>"Felix"}]
a = Array.new(2){Hash.new} # Multiple instances
a[0]['cat'] = 'feline'
a # =>[{"cat"=>"feline"},{}]
squares = Array.new(5){|i|i*i}
squares # => [0,1,4,9,16]
copy = Array.new(squares) # initialized by copying
squares[5] = 25
squares # => [0,1,4,9,16,25]
copy # => [0,1,4,9,16]
Note: the above examples taken from Programming Ruby 1.9
3 Comments
Andrew Grimm
Array.new(count, object) producing an array of the same object is a gotcha that means I avoid using that approach.
zetetic
@Andrew: not exactly in line with the "principle of least surprise", is it?
Rahul Dess
lucky that i found your answer within a minute of my doubt.
[] is a shortcut to the Array class's singleton method [] which in turn creates a new Array in just the same way as Array.new, so you could probably say 'they are the same' without worrying too much.
Note that each call to [] in irb creates a new Array:
>> [].object_id
=> 2148067340
>> [].object_id
=> 2149414040
From Ruby's C code:
rb_define_singleton_method(rb_cArray, "[]", rb_ary_s_create, -1);
Comments
Such as Hash.new vs {}. They are the same. Include speed.
Comments
There is no difference, but...
As others have already answered you
Those two statements are functionally identical
But there are guidelines to orient when you should use each one (so your code is easier to read). The reason behind that is:
Programs must be written for people to read, and only incidentally for machines to execute.
from: https://github.com/rubocop-hq/ruby-style-guide#literal-array-hash
Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).
So if you are creating an empty array [] is the best option, but if you need to create your array with a set of N nil objects, than Array.new(N) is what you should write.
Comments
There is fundamentally no difference
array.clearto achieve#=> [ ]