module Indexable(T)

Returns an Array of all ordered combinations of elements taken from each of the indexables as Arrays. Traversal of elements starts from the last Indexable. If indexables is empty, the returned product contains exactly one empty Array.

#cartesian_product is preferred over this class method when the quantity of indexables is known in advance.

Indexable.cartesian_product([[1, 2, 3], [4, 5]]) # => [[1, 4], [1, 5], [2, 4], [2, 5], [3, 4], [3, 5]]

Yields each ordered combination of the elements taken from each of the indexables as Arrays. Traversal of elements starts from the last Indexable. If indexables is empty, yields an empty Array exactly once.

#each_cartesian is preferred over this class method when the quantity of indexables is known in advance.

Indexable.each_cartesian([%w[Alice Bob Carol], [1, 2]]) do |name, n|
  puts "#{n}. #{name}"
end

Prints

1. Alice
2. Alice
1. Bob
2. Bob
1. Carol
2. Carol

By default, a new Array is created and yielded for each combination.

• If reuse is an Array, it will be reused
• If reuse is truthy, the method will create a new Array and reuse it
• If reuse is falsey, no Arrays will be reused.

This can be used to prevent many memory allocations when each combination of interest is to be used in a read-only fashion.

Returns an iterator that enumerates the ordered combinations of elements taken from the indexables as Arrays. Traversal of elements starts from the last Indexable. If indexables is empty, the returned iterator produces one empty Array, then stops.

#each_cartesian is preferred over this class method when the quantity of indexables is known in advance.

iter = Indexable.each_cartesian([%w[N S], %w[E W]])
iter.next # => ["N", "E"]
iter.next # => ["N", "W"]
iter.next # => ["S", "E"]
iter.next # => ["S", "W"]
iter.next # => Iterator::Stop::INSTANCE

By default, a new Array is created and returned for each combination.

• If reuse is an Array, it will be reused
• If reuse is truthy, the method will create a new Array and reuse it
• If reuse is falsey, no Arrays will be reused.

This can be used to prevent many memory allocations when each combination of interest is to be used in a read-only fashion.

Returns the element at the given index.

Negative indices can be used to start counting from the end of the array. Raises IndexError if trying to access an element outside the array's range.

ary = ['a', 'b', 'c']
ary[0]  # => 'a'
ary[2]  # => 'c'
ary[-1] # => 'c'
ary[-2] # => 'b'

ary[3]  # raises IndexError
ary[-4] # raises IndexError

Returns the element at the given index.

Negative indices can be used to start counting from the end of the array. Returns nil if trying to access an element outside the array's range.

ary = ['a', 'b', 'c']
ary[0]?  # => 'a'
ary[2]?  # => 'c'
ary[-1]? # => 'c'
ary[-2]? # => 'b'

ary[3]?  # nil
ary[-4]? # nil

By using binary search, returns the first element for which the passed block returns a truthy value.

If the block returns a falsey value, the element to be found lies behind. If the block returns a truthy value, the element to be found is itself or lies in front.

Binary search needs the collection to be sorted in regards to the search criterion.

Returns nil if the block didn't return a truthy value for any element.

[2, 5, 7, 10].bsearch { |x| x >= 4 } # => 5
[2, 5, 7, 10].bsearch { |x| x > 10 } # => nil

By using binary search, returns the index of the first element for which the passed block returns a truthy value.

If the block returns a falsey value, the element to be found lies behind. If the block returns a truthy value, the element to be found is itself or lies in front.

Binary search needs the collection to be sorted in regards to the search criterion.

Returns nil if the block didn't return a truthy value for any element.

[2, 5, 7, 10].bsearch_index { |x, i| x >= 4 } # => 1
[2, 5, 7, 10].bsearch_index { |x, i| x > 10 } # => nil

Returns an Array of all ordered combinations of elements taken from each of self and others as Tuples. Traversal of elements starts from the last Indexable argument.

[1, 2, 3].cartesian_product({'a', 'b'})                     # => [{1, 'a'}, {1, 'b'}, {2, 'a'}, {2, 'b'}, {3, 'a'}, {3, 'b'}]
['a', 'b'].cartesian_product({1, 2}, {'c', 'd'}).map &.join # => ["a1c", "a1d", "a2c", "a2d", "b1c", "b1d", "b2c", "b2d"]

Traverses the depth of a structure and returns the value, otherwise raises IndexError.

ary = [{1, 2, 3, {4, 5, 6}}]
ary.dig(0, 3, 2) # => 6
ary.dig(0, 3, 3) # raises IndexError

Traverses the depth of a structure and returns the value. Returns nil if not found.

ary = [{1, 2, 3, {4, 5, 6}}]
ary.dig?(0, 3, 2) # => 6
ary.dig?(0, 3, 3) # => nil

Calls the given block once for each element in self, passing that element as a parameter.

a = ["a", "b", "c"]
a.each { |x| print x, " -- " }

produces:

a -- b -- c --

Returns an Iterator for the elements of self.

a = ["a", "b", "c"]
iter = a.each
iter.next # => "a"
iter.next # => "b"

The returned iterator keeps a reference to self: if the array changes, the returned values of the iterator change as well.

Calls the given block once for count number of elements in self starting from index start, passing each element as a parameter.

Negative indices count backward from the end of the array. (-1 is the last element).

Raises IndexError if the starting index is out of range. Raises ArgumentError if count is a negative number.

array = ["a", "b", "c", "d", "e"]
array.each(start: 1, count: 3) { |x| print x, " -- " }

produces:

b -- c -- d --

Calls the given block once for all elements at indices within the given range, passing each element as a parameter.

Raises IndexError if the starting index is out of range.

array = ["a", "b", "c", "d", "e"]
array.each(within: 1..3) { |x| print x, " -- " }

produces:

b -- c -- d --

Yields each ordered combination of the elements taken from each of self and others as a Tuple. Traversal of elements starts from the last Indexable argument.

["Alice", "Bob"].each_cartesian({1, 2, 3}) do |name, n|
  puts "#{n}. #{name}"
end

Prints

1. Alice
2. Alice
3. Alice
1. Bob
2. Bob
3. Bob

Returns an iterator that enumerates the ordered combinations of elements taken from each of self and others as Tuples. Traversal of elements starts from the last Indexable argument.

iter = {1, 2, 3}.each_cartesian({'a', 'b'})
iter.next # => {1, 'a'}
iter.next # => {1, 'b'}
iter.next # => {2, 'a'}
iter.next # => {2, 'b'}
iter.next # => {3, 'a'}
iter.next # => {3, 'b'}
iter.next # => Iterator::Stop::INSTANCE

Calls the given block once for each index in self, passing that index as a parameter.

a = ["a", "b", "c"]
a.each_index { |x| print x, " -- " }

produces:

0 -- 1 -- 2 --

Returns an Iterator for each index in self.

a = ["a", "b", "c"]
iter = a.each_index
iter.next # => 0
iter.next # => 1

The returned iterator keeps a reference to self. If the array changes, the returned values of the iterator will change as well.

Calls the given block once for count number of indices in self starting from index start, passing each index as a parameter.

Negative indices count backward from the end of the array. (-1 is the last element).

Raises IndexError if the starting index is out of range. Raises ArgumentError if count is a negative number.

array = ["a", "b", "c", "d", "e"]
array.each_index(start: -3, count: 2) { |x| print x, " -- " }

produces:

2 -- 3 --

Yields each possible permutation of size of self.

a = [1, 2, 3]
sums = [] of Int32
a.each_permutation(2) { |p| sums << p.sum } # => nil
sums                                        # => [3, 4, 3, 5, 4, 5]

By default, a new array is created and yielded for each permutation. If reuse is given, the array can be reused: if reuse is an Array, this array will be reused; if reuse if truthy, the method will create a new array and reuse it. This can be used to prevent many memory allocations when each slice of interest is to be used in a read-only fashion.

Returns an Iterator over each possible permutation of size of self.

iter = [1, 2, 3].each_permutation
iter.next # => [1, 2, 3]
iter.next # => [1, 3, 2]
iter.next # => [2, 1, 3]
iter.next # => [2, 3, 1]
iter.next # => [3, 1, 2]
iter.next # => [3, 2, 1]
iter.next # => #<Iterator::Stop>

By default, a new array is created and returned for each permutation. If reuse is given, the array can be reused: if reuse is an Array, this array will be reused; if reuse if truthy, the method will create a new array and reuse it. This can be used to prevent many memory allocations when each slice of interest is to be used in a read-only fashion.

Returns true if self is empty, false otherwise.

([] of Int32).empty? # => true
([1]).empty?         # => false

Optimized version of #equals? used when other is also an Indexable.

Determines if self equals other according to a comparison done by the given block.

If self's size is the same as other's size, this method yields elements from self and other in tandem: if the block returns true for all of them, this method returns true. Otherwise it returns false.

a = [1, 2, 3]
b = ["a", "ab", "abc"]
a.equals?(b) { |x, y| x == y.size } # => true
a.equals?(b) { |x, y| x == y }      # => false

Returns the element at the given index, if in bounds, otherwise executes the given block with the index and returns its value.

a = [:foo, :bar]
a.fetch(0) { :default_value }    # => :foo
a.fetch(2) { :default_value }    # => :default_value
a.fetch(2) { |index| index * 3 } # => 6

Returns the value at the index given by index, or when not found the value given by default.

a = [:foo, :bar]
a.fetch(0, :default_value) # => :foo
a.fetch(2, :default_value) # => :default_value

:inherited:

See Object#hash(hasher)

Returns the index of the first appearance of value in self starting from the given offset, or nil if the value is not in self.

[1, 2, 3, 1, 2, 3].index(2, offset: 2) # => 4

Returns the index of the first object in self for which the block returns true, starting from the given offset, or nil if no match is found.

[1, 2, 3, 1, 2, 3].index(offset: 2) { |x| x < 2 } # => 3

Optimized version of Enumerable#join that performs better when all of the elements in this indexable are strings: the total string bytesize to return can be computed before creating the final string, which performs better because there's no need to do reallocations.

Returns the last element of self if it's not empty, or raises IndexError.

([1, 2, 3]).last   # => 3
([] of Int32).last # raises IndexError

Returns the last element of self if it's not empty, or the given block's value.

([1, 2, 3]).last { 4 }   # => 3
([] of Int32).last { 4 } # => 4

Returns the last element of self if it's not empty, or nil.

([1, 2, 3]).last?   # => 3
([] of Int32).last? # => nil

Returns an Array with all possible permutations of size.

a = [1, 2, 3]
a.permutations    # => [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
a.permutations(1) # => [[1],[2],[3]]
a.permutations(2) # => [[1,2],[1,3],[2,1],[2,3],[3,1],[3,2]]
a.permutations(3) # => [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
a.permutations(0) # => [[]]
a.permutations(4) # => []

Same as #each, but works in reverse.

Returns an Iterator over the elements of self in reverse order.

Returns the index of the last appearance of value in self, or nil if the value is not in self.

If offset is given, it defines the position to end the search (elements beyond this point are ignored).

[1, 2, 3, 2, 3].rindex(2)            # => 3
[1, 2, 3, 2, 3].rindex(2, offset: 2) # => 1

Returns the index of the first object in self for which the block returns true, starting from the last object, or nil if no match is found.

If offset is given, the search starts from that index towards the first elements in self.

[1, 2, 3, 2, 3].rindex { |x| x < 3 }            # => 3
[1, 2, 3, 2, 3].rindex(offset: 2) { |x| x < 3 } # => 1

Returns an Array of n random elements from self, using the given random number generator. All elements have equal probability of being drawn. Sampling is done without replacement; if n is larger than the size of this collection, the returned Array has the same size as self.

Raises ArgumentError if n is negative.

[1, 2, 3, 4, 5].sample(2)                # => [3, 5]
{1, 2, 3, 4, 5}.sample(2)                # => [3, 4]
{1, 2, 3, 4, 5}.sample(2, Random.new(1)) # => [1, 5]

If self is not empty and n is equal to 1, calls #sample(random) exactly once. Thus, random will be left in a different state compared to the implementation in Enumerable.

Optimized version of Enumerable#sample that runs in O(1) time.

a = [1, 2, 3]
a.sample                # => 3
a.sample                # => 1
a.sample(Random.new(1)) # => 2

Returns the number of elements in this container.

Returns an Array with all the elements in the collection.

{1, 2, 3}.to_a # => [1, 2, 3]

Returns the element at the given index, without doing any bounds check.

Indexable makes sure to invoke this method with index in 0...size, so converting negative indices to positive ones is not needed here.

Clients never invoke this method directly. Instead, they access elements with #[](index) and #[]?(index).

This method should only be directly invoked if you are absolutely sure the index is in bounds, to avoid a bounds check for a small boost of performance.

Returns a Tuple populated with the elements at the given indexes. Raises IndexError if any index is invalid.

["a", "b", "c", "d"].values_at(0, 2) # => {"a", "c"}