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Is there no difference between "size" and "length" in Ruby?

In the documentation for size

we can read here that 'size () is an alias for length'. For length

( doc ) "Returns the number of items in itself. May be zero." and this length is "Also alias as: size". The functionality may be very similar, but I'm wondering if other implementations contain any other functionality besides returning the number of elements in an array or collection. The length and size of the words seem to imply a difference, especially since size would make me think about memory size in bytes rather than number of elements.

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This is exactly the same implementation.

You can see in the Ruby 2.3.1 source code , which is an alias:

rb_define_alias(rb_cArray,  "size", "length");


Also, if you check pry and pry-doc , you can see that it is executing exactly the same code:

[1] pry(main)> list = [1,2]
=> [1, 2]
[2] pry(main)> $ list.size

From: array.c (C Method):
Owner: Array
Visibility: public
Number of lines: 6

static VALUE
rb_ary_length(VALUE ary)
{
    long len = RARRAY_LEN(ary);
    return LONG2NUM(len);
}
[3] pry(main)> $ list.length

From: array.c (C Method):
Owner: Array
Visibility: public
Number of lines: 6

static VALUE
rb_ary_length(VALUE ary)
{
    long len = RARRAY_LEN(ary);
    return LONG2NUM(len);
}
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Actually, there is a difference, but not simple Array

. If you are using ActiveRecord

Association

, there is a difference as you can see here :



  • if you have already loaded all records, say User.all

    then you should use length

    to avoid another db request

  • If you haven't downloaded anything, use count

    to make a count query on your db

  • if you don't want to bother with these considerations, use size

    which will adapt

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