Class: Rubactive::DiscreteValueStream

Inherits:
ReactiveNode show all
Defined in:
lib/rubactive/rubactive.rb

Overview

A DiscreteValueStream represents a stream of values. When a value is added to the stream, other DiscreteValueStreams may react if they follow this stream.

Streams are explicitly created with DiscreteValueStream.manual or DiscreteValueStream.follows. In the first case, values are added only with add_value. In the second, values can also be added in reaction to the streams being followed.

Streams can also be implicity created by sending other streams unrecognized messages.

origin = DiscreteValueStream.manual
follower = origin + 1

The previous definition of the follower stream is equivalent to this:

follower = DiscreteValueStream.follows(origin) { | o | o + 1 }

Constant Summary

Constants inherited from ReactiveNode

ReactiveNode::DEFAULT_VALUE

Instance Attribute Summary

Attributes inherited from ReactiveNode

#value

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from ReactiveNode

blank, #initialize, #just_values, #method_missing, #on_change, #propagate, #recalculate, #tell_earlier_nodes_about_me, #this_node_is_later_than_you

Constructor Details

This class inherits a constructor from Rubactive::ReactiveNode

Dynamic Method Handling

This class handles dynamic methods through the method_missing method in the class Rubactive::ReactiveNode

Class Method Details

.follows(*streams, &block) ⇒ Object

Create a stream that reacts to one or more other streams.

The addition of values to any of the streams will cause the block to be called with their most recent values. The result is added to this stream (as with add_value).

Example: 

origin = DiscreteValueStream.manual
follower = DiscreteValueStream.follows(origin) { | o | o+1 }
origin.add_value(5)
follower.most_recent_value #=> 6

If no block is given, this stream should be following only one other stream. The value just added to that stream is also added to this one. – Defined here so that I can write special-purpose documentation.



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# File 'lib/rubactive/rubactive.rb', line 214

def self.follows(*streams, &block)
  super
end

.manual ⇒ Object

Create an empty value stream

Use add_value to insert values into the stream.



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# File 'lib/rubactive/rubactive.rb', line 221

def self.manual
  follows {
    raise "Incorrect use of recalculation in a manual event stream"
  }
end

Instance Method Details

#add_value(new_value) ⇒ Object

Place a new value on the stream



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# File 'lib/rubactive/rubactive.rb', line 244

def add_value(new_value)    # this?
  self.value = new_value
end

#empty? ⇒ Boolean

True iff no value has ever been added to the stream.

Returns:

  • (Boolean) 


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# File 'lib/rubactive/rubactive.rb', line 249

def empty?
  most_recent_value == DEFAULT_VALUE
end

#most_recent_value ⇒ Object

Retrieve last value added to the stream

Earlier values are inaccessible.

It is an error to ask for the value of an #empty? stream.



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# File 'lib/rubactive/rubactive.rb', line 241

def most_recent_value; @value; end

#on_addition(&callback) ⇒ Object

Run a callback when a new value is added.

This is an interface to the non-reactive world. When a new value is added (whether with add_value or in reaction to a followed stream), the callback is called and given that value. The callback will typically do something with the value, like add it to a GUI.



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# File 'lib/rubactive/rubactive.rb', line 233

def on_addition(&callback); on_change(&callback); end