Operator for Iteration

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Operator For (Iteration)

Declares or defines operators used by a For...Next loop with user defined type variables

Syntax

{ Type | Class | Union } typename
Declare Operator For ()
Declare Operator For ( [ ByRef | ByVal ] stp As typename )
...
End { Type | Class | Union }

Parameters

• typename
• stp
• step_value
• typename
• iterator
• typename
• end_value
• typename
• start_value
• typename

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 For is called once after copy constructing or assigning to the iterator object, and allows the object to perform any additional initialization needed in preparation for the loop.

The first version of Operator For 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 eventual additional initialization may use 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.

See also

• Operator Next
• Operator Step
• For...Next

Examples

See the Operator Step examples.

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Category: Operators
Kind: operator

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.