Class: Enumerator

Inherits:
Object show all
Includes:
Enumerable
Defined in:
enumerator.c,
enumerator.c

Overview

A class which allows both internal and external iteration.

An Enumerator can be created by the following methods.

  • Kernel#to_enum

  • Kernel#enum_for

  • Enumerator.new

Most methods have two forms: a block form where the contents are evaluated for each item in the enumeration, and a non-block form which returns a new Enumerator wrapping the iteration.

enumerator = %w(one two three).each
puts enumerator.class # => Enumerator

enumerator.each_with_object("foo") do |item, obj|
  puts "#{obj}: #{item}"
end

# foo: one
# foo: two
# foo: three

enum_with_obj = enumerator.each_with_object("foo")
puts enum_with_obj.class # => Enumerator

enum_with_obj.each do |item, obj|
  puts "#{obj}: #{item}"
end

# foo: one
# foo: two
# foo: three

This allows you to chain Enumerators together. For example, you can map a list's elements to strings containing the index and the element as a string via:

puts %w[foo bar baz].map.with_index { |w, i| "#{i}:#{w}" }
# => ["0:foo", "1:bar", "2:baz"]

An Enumerator can also be used as an external iterator. For example, Enumerator#next returns the next value of the iterator or raises StopIteration if the Enumerator is at the end.

e = [1,2,3].each   # returns an enumerator object.
puts e.next   # => 1
puts e.next   # => 2
puts e.next   # => 3
puts e.next   # raises StopIteration

You can use this to implement an internal iterator as follows:

def ext_each(e)
  while true
    begin
      vs = e.next_values
    rescue StopIteration
      return $!.result
    end
    y = yield(*vs)
    e.feed y
  end
end

o = Object.new

def o.each
  puts yield
  puts yield(1)
  puts yield(1, 2)
  3
end

# use o.each as an internal iterator directly.
puts o.each {|*x| puts x; [:b, *x] }
# => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

# convert o.each to an external iterator for
# implementing an internal iterator.
puts ext_each(o.to_enum) {|*x| puts x; [:b, *x] }
# => [], [:b], [1], [:b, 1], [1, 2], [:b, 1, 2], 3

Direct Known Subclasses

Lazy

Defined Under Namespace

Classes: Generator, Lazy, Yielder

Instance Method Summary collapse

Methods included from Enumerable

#all?, #any?, #chunk, #collect, #collect_concat, #count, #cycle, #detect, #drop, #drop_while, #each_cons, #each_entry, #each_slice, #entries, #find, #find_all, #find_index, #first, #flat_map, #grep, #group_by, #include?, #inject, #lazy, #map, #max, #max_by, #member?, #min, #min_by, #minmax, #minmax_by, #none?, #one?, #partition, #reduce, #reject, #reverse_each, #select, #slice_before, #sort, #sort_by, #take, #take_while, #to_a, #zip

Constructor Details

#new(size = nil) {|yielder| ... } ⇒ Object #new(obj, method = :each, *args) ⇒ Object

Creates a new Enumerator object, which can be used as an Enumerable.

In the first form, iteration is defined by the given block, in which a "yielder" object, given as block parameter, can be used to yield a value by calling the yield method (aliased as <<):

fib = Enumerator.new do |y|
  a = b = 1
  loop do
    y << a
    a, b = b, a + b
  end
end

p fib.take(10) # => [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

The optional parameter can be used to specify how to calculate the size in a lazy fashion (see Enumerator#size). It can either be a value or a callable object.

In the second, deprecated, form, a generated Enumerator iterates over the given object using the given method with the given arguments passed.

Use of this form is discouraged. Use Kernel#enum_for or Kernel#to_enum instead.

e = Enumerator.new(ObjectSpace, :each_object)
    #-> ObjectSpace.enum_for(:each_object)

e.select { |obj| obj.is_a?(Class) }  #=> array of all classes

Overloads:

  • #new(size = nil) {|yielder| ... } ⇒ Object

    Yields:

    • (yielder)

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# File 'enumerator.c', line 331

static VALUE
enumerator_initialize(int argc, VALUE *argv, VALUE obj)
{
    VALUE recv, meth = sym_each;
    VALUE size = Qnil;

    if (rb_block_given_p()) {
	rb_check_arity(argc, 0, 1);
	recv = generator_init(generator_allocate(rb_cGenerator), rb_block_proc());
	if (argc) {
            if (NIL_P(argv[0]) || rb_obj_is_proc(argv[0]) ||
                (RB_TYPE_P(argv[0], T_FLOAT) && RFLOAT_VALUE(argv[0]) == INFINITY)) {
                size = argv[0];
            } else {
                size = rb_to_int(argv[0]);
            }
            argc = 0;
        }
    }
    else {
	rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
	rb_warn("Enumerator.new without a block is deprecated; use Object#to_enum");
	recv = *argv++;
	if (--argc) {
	    meth = *argv++;
	    --argc;
	}
    }

    return enumerator_init(obj, recv, meth, argc, argv, 0, size);
}

Instance Method Details

#each { ... } ⇒ Object

Iterates over the block according to how this Enumerable was constructed. If no block is given, returns self.

Yields:


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# File 'enumerator.c', line 441

static VALUE
enumerator_each(int argc, VALUE *argv, VALUE obj)
{
    if (argc > 0) {
	struct enumerator *e = enumerator_ptr(obj = rb_obj_dup(obj));
	VALUE args = e->args;
	if (args) {
	    args = rb_ary_dup(args);
	    rb_ary_cat(args, argv, argc);
	}
	else {
	    args = rb_ary_new4(argc, argv);
	}
	e->args = args;
    }
    if (!rb_block_given_p()) return obj;
    return enumerator_block_call(obj, 0, obj);
}

#each_with_index {|(*args), idx| ... } ⇒ Object #each_with_indexObject

Same as Enumerator#with_index(0), i.e. there is no starting offset.

If no block is given, a new Enumerator is returned that includes the index.

Overloads:

  • #each_with_index {|(*args), idx| ... } ⇒ Object

    Yields:

    • ((*args), idx)

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# File 'enumerator.c', line 511

static VALUE
enumerator_each_with_index(VALUE obj)
{
    return enumerator_with_index(0, NULL, obj);
}

#with_object(obj) {|(*args), obj| ... } ⇒ Object #with_object(obj) ⇒ Object

Iterates the given block for each element with an arbitrary object, obj, and returns obj

If no block is given, returns a new Enumerator.

Example

to_three = Enumerator.new do |y|
  3.times do |x|
    y << x
  end
end

to_three_with_string = to_three.with_object("foo")
to_three_with_string.each do |x,string|
  puts "#{string}: #{x}"
end

# => foo:0
# => foo:1
# => foo:2

Overloads:

  • #with_object(obj) {|(*args), obj| ... } ⇒ Object

    Yields:

    • ((*args), obj)

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# File 'enumerator.c', line 553

static VALUE
enumerator_with_object(VALUE obj, VALUE memo)
{
    RETURN_SIZED_ENUMERATOR(obj, 1, &memo, enumerator_size);
    enumerator_block_call(obj, enumerator_with_object_i, memo);

    return memo;
}

#objnil

Sets the value to be returned by the next yield inside e.

If the value is not set, the yield returns nil.

This value is cleared after being yielded.

o = Object.new
def o.each
  x = yield         # (2) blocks
  p x               # (5) => "foo"
  x = yield         # (6) blocks
  p x               # (8) => nil
  x = yield         # (9) blocks
  p x               # not reached w/o another e.next
end

e = o.to_enum
e.next              # (1)
e.feed "foo"        # (3)
e.next              # (4)
e.next              # (7)
                    # (10)

Returns:

  • (nil)

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# File 'enumerator.c', line 836

static VALUE
enumerator_feed(VALUE obj, VALUE v)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->feedvalue != Qundef) {
	rb_raise(rb_eTypeError, "feed value already set");
    }
    e->feedvalue = v;

    return Qnil;
}

#initialize_copyObject

:nodoc:


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# File 'enumerator.c', line 364

static VALUE
enumerator_init_copy(VALUE obj, VALUE orig)
{
    struct enumerator *ptr0, *ptr1;

    if (!OBJ_INIT_COPY(obj, orig)) return obj;
    ptr0 = enumerator_ptr(orig);
    if (ptr0->fib) {
	/* Fibers cannot be copied */
	rb_raise(rb_eTypeError, "can't copy execution context");
    }

    TypedData_Get_Struct(obj, struct enumerator, &enumerator_data_type, ptr1);

    if (!ptr1) {
	rb_raise(rb_eArgError, "unallocated enumerator");
    }

    ptr1->obj  = ptr0->obj;
    ptr1->meth = ptr0->meth;
    ptr1->args = ptr0->args;
    ptr1->fib  = 0;
    ptr1->lookahead  = Qundef;
    ptr1->feedvalue  = Qundef;
    ptr1->size  = ptr0->size;
    ptr1->size_fn  = ptr0->size_fn;

    return obj;
}

#inspectString

Creates a printable version of e.

Returns:


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# File 'enumerator.c', line 954

static VALUE
enumerator_inspect(VALUE obj)
{
    return rb_exec_recursive(inspect_enumerator, obj, 0);
}

#nextObject

Returns the next object in the enumerator, and move the internal position forward. When the position reached at the end, StopIteration is raised.

Example

a = [1,2,3]
e = a.to_enum
p e.next   #=> 1
p e.next   #=> 2
p e.next   #=> 3
p e.next   #raises StopIteration

Note that enumeration sequence by next does not affect other non-external enumeration methods, unless the underlying iteration methods itself has side-effect, e.g. IO#each_line.

Returns:


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# File 'enumerator.c', line 727

static VALUE
enumerator_next(VALUE obj)
{
    VALUE vs = enumerator_next_values(obj);
    return ary2sv(vs, 0);
}

#next_valuesArray

Returns the next object as an array in the enumerator, and move the internal position forward. When the position reached at the end, StopIteration is raised.

This method can be used to distinguish yield and yield nil.

Example

o = Object.new
def o.each
  yield
  yield 1
  yield 1, 2
  yield nil
  yield [1, 2]
end
e = o.to_enum
p e.next_values
p e.next_values
p e.next_values
p e.next_values
p e.next_values
e = o.to_enum
p e.next
p e.next
p e.next
p e.next
p e.next

## yield args       next_values      next
#  yield            []               nil
#  yield 1          [1]              1
#  yield 1, 2       [1, 2]           [1, 2]
#  yield nil        [nil]            nil
#  yield [1, 2]     [[1, 2]]         [1, 2]

Note that next_values does not affect other non-external enumeration methods unless underlying iteration method itself has side-effect, e.g. IO#each_line.

Returns:


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# File 'enumerator.c', line 670

static VALUE
enumerator_next_values(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);
    VALUE vs;

    if (e->lookahead != Qundef) {
        vs = e->lookahead;
        e->lookahead = Qundef;
        return vs;
    }

    return get_next_values(obj, e);
}

#peekObject

Returns the next object in the enumerator, but doesn't move the internal position forward. If the position is already at the end, StopIteration is raised.

Example

a = [1,2,3]
e = a.to_enum
p e.next   #=> 1
p e.peek   #=> 2
p e.peek   #=> 2
p e.peek   #=> 2
p e.next   #=> 2
p e.next   #=> 3
p e.next   #raises StopIteration

Returns:


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# File 'enumerator.c', line 801

static VALUE
enumerator_peek(VALUE obj)
{
    VALUE vs = enumerator_peek_values(obj);
    return ary2sv(vs, 1);
}

#peek_valuesArray

Returns the next object as an array, similar to Enumerator#next_values, but doesn't move the internal position forward. If the position is already at the end, StopIteration is raised.

Example

o = Object.new
def o.each
  yield
  yield 1
  yield 1, 2
end
e = o.to_enum
p e.peek_values    #=> []
e.next
p e.peek_values    #=> [1]
p e.peek_values    #=> [1]
e.next
p e.peek_values    #=> [1, 2]
e.next
p e.peek_values    # raises StopIteration

Returns:


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# File 'enumerator.c', line 773

static VALUE
enumerator_peek_values_m(VALUE obj)
{
    return rb_ary_dup(enumerator_peek_values(obj));
}

#rewindObject

Rewinds the enumeration sequence to the beginning.

If the enclosed object responds to a "rewind" method, it is called.


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# File 'enumerator.c', line 858

static VALUE
enumerator_rewind(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    rb_check_funcall(e->obj, id_rewind, 0, 0);

    e->fib = 0;
    e->dst = Qnil;
    e->lookahead = Qundef;
    e->feedvalue = Qundef;
    e->stop_exc = Qfalse;
    return obj;
}

#sizeInteger, ...

Returns the size of the enumerator, or nil if it can't be calculated lazily.

(1..100).to_a.permutation(4).size # => 94109400
loop.size # => Float::INFINITY
(1..100).drop_while.size # => nil

Returns:


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# File 'enumerator.c', line 971

static VALUE
enumerator_size(VALUE obj)
{
    struct enumerator *e = enumerator_ptr(obj);

    if (e->size_fn) {
	return (*e->size_fn)(e->obj, e->args, obj);
    }
    if (rb_obj_is_proc(e->size)) {
        if (e->args)
	    return rb_proc_call(e->size, e->args);
        else
            return rb_proc_call_with_block(e->size, 0, 0, Qnil);
    }
    return e->size;
}

#with_index(offset = 0) {|(*args), idx| ... } ⇒ Object #with_index(offset = 0) ⇒ Object

Iterates the given block for each element with an index, which starts from offset. If no block is given, returns a new Enumerator that includes the index, starting from offset

offset

the starting index to use

Overloads:

  • #with_index(offset = 0) {|(*args), idx| ... } ⇒ Object

    Yields:

    • ((*args), idx)

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# File 'enumerator.c', line 490

static VALUE
enumerator_with_index(int argc, VALUE *argv, VALUE obj)
{
    VALUE memo;

    rb_scan_args(argc, argv, "01", &memo);
    RETURN_SIZED_ENUMERATOR(obj, argc, argv, enumerator_size);
    memo = NIL_P(memo) ? 0 : (VALUE)NUM2LONG(memo);
    return enumerator_block_call(obj, enumerator_with_index_i, (VALUE)&memo);
}

#with_object(obj) {|(*args), obj| ... } ⇒ Object #with_object(obj) ⇒ Object

Iterates the given block for each element with an arbitrary object, obj, and returns obj

If no block is given, returns a new Enumerator.

Example

to_three = Enumerator.new do |y|
  3.times do |x|
    y << x
  end
end

to_three_with_string = to_three.with_object("foo")
to_three_with_string.each do |x,string|
  puts "#{string}: #{x}"
end

# => foo:0
# => foo:1
# => foo:2

Overloads:

  • #with_object(obj) {|(*args), obj| ... } ⇒ Object

    Yields:

    • ((*args), obj)

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# File 'enumerator.c', line 553

static VALUE
enumerator_with_object(VALUE obj, VALUE memo)
{
    RETURN_SIZED_ENUMERATOR(obj, 1, &memo, enumerator_size);
    enumerator_block_call(obj, enumerator_with_object_i, memo);

    return memo;
}