Class: ScanLeft

Inherits:

Object

• Object
• ScanLeft

Defined in:

lib/scan_left.rb,
lib/scan_left/version.rb

Overview

Wraps any Enumerable to provide the #scan_left operation.

Please see README for details, examples, background, and further reading about this operation.

Note: if you’d prefer to use the #scan_left method directly on any Enumerable instance, please see the optional refinement EnumerableWithScanLeft.

Examples:

ScanLeft.new([1, 2, 3]).scan_left(0) { |s, x| s + x } == [0, 1, 3, 6]

See Also:

• EnumerableWithScanLeft

Constant Summary

VERSION =

"0.3.1"

Instance Attribute Summary

• #enumerable ⇒ Enumerable readonly

  Enumerable to transform via #scan_left.

Instance Method Summary

• #initialize(enumerable) ⇒ ScanLeft constructor

  A new instance of ScanLeft.

• #scan_left(initial) {|memo, obj| ... } ⇒ Enumerable

  Map the enumerable to the incremental state of a calculation by applying the given block, in turn, to each element and the previous state of the calculation, resulting in an enumerable of the state after each iteration.

Constructor Details

#initialize(enumerable) ⇒ ScanLeft

Returns a new instance of ScanLeft.

Parameters:

• enumerable (Enumerable) —

  Enumerable to transform via #scan_left

# File 'lib/scan_left.rb', line 26

def initialize(enumerable)
  @enumerable = enumerable
end

Instance Attribute Details

#enumerable ⇒ Enumerable (readonly)

Returns Enumerable to transform via #scan_left.

Returns:

• (Enumerable) —

  Enumerable to transform via #scan_left

# File 'lib/scan_left.rb', line 23

def enumerable
  @enumerable
end

Instance Method Details

#scan_left(initial) {|memo, obj| ... } ⇒ Enumerable

Map the enumerable to the incremental state of a calculation by applying the given block, in turn, to each element and the previous state of the calculation, resulting in an enumerable of the state after each iteration.

Parameters:

• initial (Object) —

  Initial state value to yield.

Yields:

• (memo, obj) —

  Invokes given block with previous state value memo and next element of the stream obj.

Yield Returns:

• (Object) —

  The next state value for memo.

Returns:

• (Enumerable) —

  Generate a stream of intermediate states resulting from applying a binary operator. Equivalent to a stream of #inject calls on first N elements, increasing N from zero to the size of the stream. NOTE: Preserves laziness if enumerable is lazy.

# File 'lib/scan_left.rb', line 47

def scan_left(initial)
  memo = initial
  outs = enumerable.map { |*obj| memo = yield(memo, *obj) }
  prepend_preserving_laziness(value: initial, enum: outs)
end