Class: Axiom::Relation::Operation::Offset

Inherits:

Axiom::Relation

• Object
• Axiom::Relation
• Axiom::Relation::Operation::Offset

Includes:

Unary

Defined in:

lib/axiom/relation/operation/offset.rb

Overview

A class representing an offset relation

Defined Under Namespace

Modules: Methods

Instance Attribute Summary

• #directions ⇒ Operation::Sorted::DirectionSet readonly private

  The relation sort order.

• #offset ⇒ Integer readonly

  Return the offset.

Attributes included from Operation::Unary

#operand

Attributes inherited from Axiom::Relation

#header

Class Method Summary

• .new(operand, offset) ⇒ Offset

  Instantiate a new Offset.

Instance Method Summary

• #delete ⇒ undefined

  Raise an exception when deleting from the Offset.

• #each {|tuple| ... } ⇒ self

  Iterate over each tuple in the set.

• #initialize(operand, offset) ⇒ undefined constructor private

  Initialize an Offset.

• #insert ⇒ undefined

  Raise an exception when inserting into the Offset.

Methods inherited from Axiom::Relation

#==, #[], #empty?, #include?, #materialize, #materialized?, #replace

Methods included from Visitable

#accept

Constructor Details

#initialize(operand, offset) ⇒ undefined

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Initialize an Offset

Parameters:

• operand (Relation) —

  the relation to offset

• offset (Integer) —

  the offset of the operand to drop

# File 'lib/axiom/relation/operation/offset.rb', line 92

def initialize(operand, offset)
  super(operand)
  @offset     = offset
  @directions = operand.directions
end

Instance Attribute Details

#directions ⇒ Operation::Sorted::DirectionSet (readonly)

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

The relation sort order

Returns:

• (Operation::Sorted::DirectionSet)

# File 'lib/axiom/relation/operation/offset.rb', line 27

def directions
  @directions
end

#offset ⇒ Integer (readonly)

Return the offset

Examples:

offset = offset_relation.offset

Returns:

• (Integer)

# File 'lib/axiom/relation/operation/offset.rb', line 20

def offset
  @offset
end

Class Method Details

.new(operand, offset) ⇒ Offset

Instantiate a new Offset

Examples:

offset_relation = Offset.new(operand, offset)

Parameters:

• operand (Relation) —

  the relation to offset

• offset (Integer) —

  the offset of the operand to drop

Returns:

• (Offset)

# File 'lib/axiom/relation/operation/offset.rb', line 42

def self.new(operand, offset)
  assert_sorted_operand(operand)
  assert_valid_offset(offset)
  super
end

Instance Method Details

#delete ⇒ undefined

Raise an exception when deleting from the Offset

Examples:

offset.delete(other)  # => ImmutableRelationError raised

Returns:

• (undefined)

Raises:

• (ImmutableRelationError) —

  raised when deleting from the offset

# File 'lib/axiom/relation/operation/offset.rb', line 146

def delete(*)
  fail ImmutableRelationError, 'deleting from an offset is impossible'
end

#each {|tuple| ... } ⇒ self

Iterate over each tuple in the set

Examples:

offset_relation = Offset.new(operand, offset)
offset_relation.each { |tuple| ... }

Yields:

• (tuple)

Yield Parameters:

• tuple (Tuple) —

  each tuple in the set

Returns:

• (self)

# File 'lib/axiom/relation/operation/offset.rb', line 112

def each
  return to_enum unless block_given?
  operand.each_with_index do |tuple, index|
    yield tuple if index >= @offset
  end
  self
end

#insert ⇒ undefined

Raise an exception when inserting into the Offset

Examples:

offset.insert(other)  # => ImmutableRelationError raised

Returns:

• (undefined)

Raises:

• (ImmutableRelationError) —

  raised when inserting into the offset

# File 'lib/axiom/relation/operation/offset.rb', line 131

def insert(*)
  fail ImmutableRelationError, 'inserting into an offset is impossible'
end