Accumulator passing

Intent

Use of an accumulator variable to allow the finer control over the assembly of the final result of an algorithm

Motivation

We want to use method-chaining, but we need to return values from some of the methods

Implementation

Use an accumulator variable

Example

a simple IFS( iterative function system )
x(t+1) = x(t) + f[random(1..i)]( 1/(t+1) )
note: the implementation is quite naive and not foolproof at all.

<php
class example {
  private $ifs = array( 'sin', 'cos' );  

  function x( &$acc ) {
    $acc['t'] += 1;
    $acc['x'] = $acc['x'] + $this->ifs[ rand(0,1) ]( 1/ $acc['t'] );
    return $this;
  }
}

$ex = new example();

$something = array('t'=>0, 'x' => 0 );
$ex->x($something) -> x($something) -> x($something);
print 't: ' . $something['t'] . ' x: ' . $something['x'] . "\n";
?>

and when you run it:

vlado@cow:~/php design patterns$ php  php accumulator_passing.php
t: 3 x:1.34692254127
vlado@cow:~/php design patterns$ php accumulator_passing.php
t: 3 x: 1.64809122021
vlado@cow:~/php design patterns$ php accumulator_passing.php
t: 3 x: 2.66401049301