Is it ok to use `any?` to check if an array is not empty?

Avoid any? for large arrays.

• any? is O(n)
• empty? is O(1)

any? does not check the length but actually scans the whole array for truthy elements.

static VALUE
rb_ary_any_p(VALUE ary)
{
  long i, len = RARRAY_LEN(ary);
  const VALUE *ptr = RARRAY_CONST_PTR(ary);

  if (!len) return Qfalse;
  if (!rb_block_given_p()) {
    for (i = 0; i < len; ++i) if (RTEST(ptr[i])) return Qtrue;
  }
  else {
    for (i = 0; i < RARRAY_LEN(ary); ++i) {
        if (RTEST(rb_yield(RARRAY_AREF(ary, i)))) return Qtrue;
    }
  }
  return Qfalse;
}

empty? on the other hand checks the length of the array only.

static VALUE
rb_ary_empty_p(VALUE ary)
{
  if (RARRAY_LEN(ary) == 0)
    return Qtrue;
  return Qfalse;
}

The difference is relevant if you have "sparse" arrays that start with lots of nil values, like for example an array that was just created.

any? isn't the same as not empty? in some cases.

>> [nil, 1].any?
=> true
>> [nil, nil].any?
=> false

From the documentation:

If the block is not given, Ruby adds an implicit block of {|obj| obj} (that is any? will return true if at least one of the collection members is not false or nil).

Prefixing the statement with an exclamation mark will let you know whether the array is not empty. So in your case -

a = [1,2,3]
!a.empty?
=> true

The difference between an array evaluating its values to true or if its empty.

The method empty? comes from the Array class
http://ruby-doc.org/core-2.0.0/Array.html#method-i-empty-3F

It's used to check if the array contains something or not. This includes things that evaluate to false, such as nil and false.

>> a = []
=> []
>> a.empty?
=> true
>> a = [nil, false]
=> [nil, false]
>> a.empty?
=> false
>> a = [nil]
=> [nil]
>> a.empty?
=> false

---

The method any? comes from the Enumerable module.
http://ruby-doc.org/core-2.0.0/Enumerable.html#method-i-any-3F

It's used to evaluate if "any" value in the array evaluates to true. Similar methods to this are none?, all? and one?, where they all just check to see how many times true could be evaluated. which has nothing to do with the count of values found in a array.

case 1

>> a = []
=> []
>> a.any?
=> false
>> a.one?
=> false
>> a.all?
=> true
>> a.none?
=> true

case 2

>> a = [nil, true]
=> [nil, true]
>> a.any?
=> true
>> a.one?
=> true
>> a.all?
=> false
>> a.none?
=> false

case 3

>> a = [true, true]
=> [true, true]
>> a.any?
=> true
>> a.one?
=> false
>> a.all?
=> true
>> a.none?
=> false