Increment the value of the named field

Contract
Return type	wob
Parameter key	Default value	Type
a_key	req
step	1	integer
if_missing	"error"	type.<one_of "error" "create"/>

Water Contract
<method increment a_key =req step =1 if_missing="error"=<type.one_of "error" "create"/>/>

See also: copy_down_data, plus

Adds the value of step to the value of the field identified by _subject.a_key . _subject defaults to the local environment.

<set x=6>
 <increment "x" />
</set>

Notice that a_key is passed as a string . To be able to use increment on an inherited field, the field should be copied down from the parent class using copy_down_data . Attempting to call increment on an inherited field without copying it down will result in a "field not found" error.

Example: Data not copied down

<class foo bar=20 />
<set a=<foo /> />
<try if_error="field not found">
 a.<increment "bar" />
</try>

"field not found"

Example: Data copied down

<class foo bar=20 >
 <method make>
    .<copy_down_data />
    _subject
 </method>
</class>
<set a=<foo /> />
<try if_error="field not found">
 a.<increment "bar" />
</try>

a wob
Parameter key Default value Type
step 1 integer
This field sets the "step value", the amount to add to the current value.

Example: Add 2 by incrementing

<set x=6>
 <increment "x" step=2 />
</set>

a wob
Parameter key Default value Type
if_missing "error" type.<one_of "error" "create"/>
Whenever a field lookup is performed in Water there is a chance that the field will not be found. If the field is "missing", Water can take various actions to try to fix the situation. increment provides two possible values for if_missing.

a wob

if_missing="error"

If a_key is not found, throw an error.

<try if_error="error">
<set x=6>
 <increment "y" />
</set>
</try>

"error"

a wob

if_missing="create"

If a_key is not found, create the key, set it to zero, and add the step value..

<try if_error="error">
<set x=6>
 <increment "y" step=2 if_missing="create" />
</set>
</try>