Operator Step (Iteration)
Increments the iterator of a For...Next loop
For iterator [ As typename ] = start_value To end_value [ Step step_value ]
typename
stp, step_value
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.
Operator Step is called to increment the iterator immediately after all statements in the For...Next body are executed, if any.
The first version of Operator Step 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.
A more practical example demonstrating file iteration based on cha0s' file iteration class.
Syntax
Usage
For iterator [ As typename ] = start_value To end_value [ Step step_value ]
[ ...statements... ]
NextParameters
typename
stp, step_value
a typename object used as an incremental value
iteratora typename object used as an iterator
end_valuea typename object used as a loop-terminating value
start_valuea 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.
Operator Step is called to increment the iterator immediately after all statements in the For...Next body are executed, if any.
The first version of Operator Step 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.
Example
'' Example Type
Type T
'' value is set by the constructor
value As Double
Declare Constructor( ByVal x As Double = 0 )
Declare Operator For( ByRef stp As T )
Declare Operator Step( ByRef stp As T )
Declare Operator Next( ByRef cond As T, ByRef stp As T ) As Integer
End Type
Constructor T ( ByVal x As Double )
Print "T iterator constructed with value " & x
value = x
End Constructor
Operator T.for( ByRef stp As T )
End Operator
Operator T.step( ByRef stp As T )
Print " incremented by " & stp.value & " in step."
value += stp.value
End Operator
Operator T.next( ByRef cond As T, ByRef stp As T ) As Integer
'' iterator's moving from a high value to a low value (step >= 0)
If( stp.value < 0 ) Then
Return( value >= cond.value )
Else
'' iterator's moving from a low value to a high value (step < 0)
Return( value <= cond.value )
End If
End Operator
'' Example Usage. It looks like we are working with numbers, but the iterators
'' have overloaded constructors. The 10, 1, and -1 are all of type T.
For i As T = 10 To 1 Step -1
Print i.value;
Next i
Type T
'' value is set by the constructor
value As Double
Declare Constructor( ByVal x As Double = 0 )
Declare Operator For( ByRef stp As T )
Declare Operator Step( ByRef stp As T )
Declare Operator Next( ByRef cond As T, ByRef stp As T ) As Integer
End Type
Constructor T ( ByVal x As Double )
Print "T iterator constructed with value " & x
value = x
End Constructor
Operator T.for( ByRef stp As T )
End Operator
Operator T.step( ByRef stp As T )
Print " incremented by " & stp.value & " in step."
value += stp.value
End Operator
Operator T.next( ByRef cond As T, ByRef stp As T ) As Integer
'' iterator's moving from a high value to a low value (step >= 0)
If( stp.value < 0 ) Then
Return( value >= cond.value )
Else
'' iterator's moving from a low value to a high value (step < 0)
Return( value <= cond.value )
End If
End Operator
'' Example Usage. It looks like we are working with numbers, but the iterators
'' have overloaded constructors. The 10, 1, and -1 are all of type T.
For i As T = 10 To 1 Step -1
Print i.value;
Next i
A more practical example demonstrating file iteration based on cha0s' file iteration class.
'' a class which iterates through files
Type FileIter
As String pathName, fileName
Declare Constructor( ByRef pathName As String )
Declare Operator For()
Declare Operator Step()
Declare Operator Next( ByRef endCond As FileIter) As Integer
End Type
Constructor FileIter( ByRef pathName As String )
this.pathName = pathName
End Constructor
Operator FileIter.for( )
fileName = Dir(pathName & "/*.*")
End Operator
Operator FileIter.step( )
fileName = Dir("")
End Operator
Operator FileIter.next( ByRef endCond As FileIter ) As Integer
Return(fileName <> endCond.pathName)
'' the c'tor sets the path name and so we check against that
End Operator
'' example code
'' change it to any directory
For i As FileIter = "./" To ""
Print i.fileName
Next
Type FileIter
As String pathName, fileName
Declare Constructor( ByRef pathName As String )
Declare Operator For()
Declare Operator Step()
Declare Operator Next( ByRef endCond As FileIter) As Integer
End Type
Constructor FileIter( ByRef pathName As String )
this.pathName = pathName
End Constructor
Operator FileIter.for( )
fileName = Dir(pathName & "/*.*")
End Operator
Operator FileIter.step( )
fileName = Dir("")
End Operator
Operator FileIter.next( ByRef endCond As FileIter ) As Integer
Return(fileName <> endCond.pathName)
'' the c'tor sets the path name and so we check against that
End Operator
'' example code
'' change it to any directory
For i As FileIter = "./" To ""
Print i.fileName
Next
Dialect Differences
- Only available in the -lang fb dialect.
See also
