Operator Next (Iteration)operator

Determines if a For...Next loop should be terminated

Operatorsoperatordocumented

Syntax

{ Type | Class | Union } typename

Declare Operator Next ( [ ByRef | ByVal ] cond As typename ) As Integer

Declare Operator Next ( [ ByRef | ByVal ] cond As typename, [ ByRef | ByVal ] stp As typename ) As Integer

...

End { Type | Class | Union }

Parameters

Name		Description
`typename`		name of the `Type`, `Class`, or `Union`
`cond`		,
`end_value`		a
`typename`		object used as a loop-terminating value
`stp`		,
`step_value`		a
`typename`		object used as an incremental value
`iterator`		a
`typename`		object used as an iterator
`start_value`		a
`typename`		object used to copy construct or assign to the iterator initially

Description

Operator For, Operator Next and Operator Step can be overloaded in user-defined type definitions to allow objects of that type to be used as iterators and step values in For...Next loops.
As all non-static member procedures, they have passed a hidden This parameter that allows to access by reference to the iterator object in the code body of the 3 operators.

Operator Next is called every time the iterator object needs to be checked against the end value. This happens immediately after the call to its Operator For, and immediately after any calls to its Operator Step. Operator Next should return zero (0) if the loop should be terminated, or non-zero if the loop should continue iterating. The first time Operator Next is called, no statements in the For...Next body, if any, have been executed yet.

The first version of Operator Next is used if no step value is given in the For...Next statement. If a step value is given, the second version is used and is passed the step value because testing for iterating end may depend on it.

Advanced usage

The above description seems to imply that the 3 arguments start_value, end_value, and step_value must be of the same type as the iterator (this is the more obvious use), but it is not quite true:

- The start_value, end_value, and step_value arguments can be of any type (of different types among themselves and also of different types from the one of the iterator).
- The only constraint is that the iterator could be constructed (in case of local iterator) or assigned (in case of global iterator) from the start_value argument (because the iterator is implicitly constructed or assigned under the hood).
- Similarly the other parameters end_value, and step_value must be able to be converted into objects of the same type as the iterator.

Remarks

Usage



For iterator [ As typename ] = start_value To end_value [ Step step_value ]

[ ...statements... ]

Next

Dialect Differences

Only available in the -lang fb dialect.

Example

See the Operator Step examples.

Reference

Documented in KeyPgOpNext.html