Increments or decrements the value found in a process variable or a workitem field.

One points to a var or a field in these various ways :

  sequence do
    inc :var => 'counter'
    inc :field => 'counter'
    inc 'v:counter'
    inc 'f:counter'
  end

‘inc’ and ‘dec’ work with two types of values : numbers (the default) and arrays.

numbers

The vanilla case of inc/dec is increasing/decreasing a value by 1.

  dec :var => 'x'

will decrease the value in variable ‘x’ by 1.

inc/dec works with two kind of numbers, integers and floats.

If the target var or field is not set, it will be assumed to be at zero.

The default increment is 1 (or 1.0 for floats). It can be changed by passing a value to the inc/dec expression.

  inc 'v:x', :val => 3
  inc 'v:y', :val => 2.4

arrays

inc/dec can be used to push/pop elements in arrays held in process variables or workitem fields.

This fragment of process definition

  sequence do
    set 'v:x' => %w[ a b c d ]
    repeat do
      dec 'v:x', :pos => 'head'
      _break :unless => '${v:d}'
      participant '${v:d}'
    end
  end

is equivalent to

  iterator :on => 'a, b, c, d', :to_var => 'x' do
    participant '${v:x}'
  end

More details : the inc expression expects a value and it will place it at the end of the current array. The :pos or :position attribute can be set to ‘head’ to let the inc expression place the value at the head of the array.

  set 'v:x' => [ 'alfred', 'bryan' ]
  set 'v:customer_name' => 'charles'

  inc 'v:x', :val => '${v:customer_name}'
    # the variable 'x' now holds [ 'alfred', 'bryan', 'charles' ]
  inc 'v:y', :val => '${v:customer_name}', :pos => 'head'
    # the variable 'x' now holds [ 'charles', 'alfred', 'bryan', 'charles' ]

The ‘dec’ / ‘decrement’ variant of the expression will remove the tail value (by default) of the array, or the head value if :pos is set to ‘head’.

It‘s also possible to remove a specific value by passing it to ‘dec’ :

  set 'v:x' => [ 'alfred', 'bryan', 'carl' ]
  dec 'v:x', :val => 'bryan'
    # the variable 'x' now holds [ 'alfred', 'carl' ]

‘dec’ places the removed value in the local variable named ‘d’. This trick was used in the above iterator example.

A specific variable or field can be specified via the :to_var / :to_field attributes :

  dec 'v:x', :to_v => 'a'
  participant :ref => '${v:a}'