EXTENDS ZSTRING
Specifies a type which inherits a Zstring behavior
Syntax:
Description:
Extends Zstring declares typename to inherit properties and behaviors of a Zstring. Purpose is to allow users to create custom string types (with i.e. dynamic memory management) that can integrate well in to existing fbc compiler built ins (good interoperability with fbc's Zstring type).
This declaration of such a UDT with a suitable Cast operator will instruct compiler to convert the UDT to a Zstring (in addition, other suitable operators as Let, [] (Pointer index), Len, ..., can be also declared).
Zstring behaviour can be inherited directly, or indirectly and singly from a base-type.
Zstring behaviour can be inherited by a UDT also extending base_typename (a kind of pseudo multiple-inheritance).
By declaring a type (directly or indirectly) as Extends Zstring (in addition to defining a suitable Cast operator only), this promotes it fully Zstring type compatible, even with Strptr/Sadd, Lset/Rset, and Select Case.
This declaration of such a UDT with a suitable Cast operator will instruct compiler to convert the UDT to a Zstring (in addition, other suitable operators as Let, [] (Pointer index), Len, ..., can be also declared).
Zstring behaviour can be inherited directly, or indirectly and singly from a base-type.
Zstring behaviour can be inherited by a UDT also extending base_typename (a kind of pseudo multiple-inheritance).
By declaring a type (directly or indirectly) as Extends Zstring (in addition to defining a suitable Cast operator only), this promotes it fully Zstring type compatible, even with Strptr/Sadd, Lset/Rset, and Select Case.
Examples:
Type myZstring Extends ZString
Public:
Declare Constructor (ByRef z As Const ZString = "")
Declare Operator Cast () ByRef As Const ZString
Declare Operator Let (ByRef z As Const ZString)
Private:
Dim As String s
End Type
Constructor myZstring (ByRef z As Const ZString = "")
This.s = z
End Constructor
Operator myZstring.Cast () ByRef As Const ZString
Return *StrPtr(This.s)
End Operator
Operator myZstring.Let (ByRef z As Const ZString)
This.s = z
End Operator
Dim As myZstring z = "FreeBASIC"
Print "'" & z & "'"
z &= " compiler"
Print "'" & z & "'"
Sleep
Public:
Declare Constructor (ByRef z As Const ZString = "")
Declare Operator Cast () ByRef As Const ZString
Declare Operator Let (ByRef z As Const ZString)
Private:
Dim As String s
End Type
Constructor myZstring (ByRef z As Const ZString = "")
This.s = z
End Constructor
Operator myZstring.Cast () ByRef As Const ZString
Return *StrPtr(This.s)
End Operator
Operator myZstring.Let (ByRef z As Const ZString)
This.s = z
End Operator
Dim As myZstring z = "FreeBASIC"
Print "'" & z & "'"
z &= " compiler"
Print "'" & z & "'"
Sleep
Type vZstring Extends ZString
Public:
Declare Constructor (ByVal pz As Const ZString Ptr = 0)
Declare Operator Cast () ByRef As ZString
Declare Operator Let (ByVal pz As Const ZString Ptr)
Declare Operator [] (ByVal index As Integer) ByRef As UByte
Declare Destructor ()
Private:
Dim As ZString Ptr p
Dim As UInteger l
End Type
Constructor vZstring (ByVal pz As Const ZString Ptr = 0)
This.l = Len(*pz)
This.p = CAllocate(This.l + 1, SizeOf(ZString))
*This.p = *pz
End Constructor
Operator vZstring.Cast () ByRef As ZString
Return *This.p
End Operator
Operator vZstring.Let (ByVal pz As Const ZString Ptr)
If This.l < Len(*pz) Then
Deallocate(This.p)
This.l = Len(*pz)
This.p = CAllocate(This.l + 1, SizeOf(ZString))
End If
*This.p = *pz
End Operator
Operator vZstring.[] (ByVal index As Integer) ByRef As UByte
Return This.p[index]
End Operator
Destructor vZstring ()
Deallocate(This.p)
End Destructor
Operator Len (ByRef v As vZstring) As Integer
Return Len(Type<String>(v)) '' found nothing better than this
End Operator '' (or: 'Return Len(Str(v))')
Dim As vZstring v = "FreeBASIC"
Print "'" & v & "'", Len(v)
Dim As ZString * 256 z
z = *StrPtr(v) '' 'error 24: Invalid data types' without 'Extends Zstring'
Print "'" & z & "'", Len(z)
v &= Space(2)
Print "'" & v & "'", Len(v)
RSet v, "FreeBASIC" '' 'error 24: Invalid data types' without 'Extends Zstring'
Print "'" & v & "'", Len(v) '' ('Cast' must return a modifiable reference)
Select Case v '' 'error 24: Invalid data types' without 'Extends Zstring'
Case Type<vZstring>(Trim(v) & " ")
Print "Left justified"
Case Type<vZstring>(" " & Trim(v))
Print "Right justified"
End Select
v[0] = Asc("-")
Print "'" & v & "'", Len(v)
Print "'" & Right(v, 5) & "'" '' since fbc 1.09.0, 'Right' supports types with 'Extends Zstring'
'Print "'" & Right(Str(v), 5) & "'" '' before fbc 1.09.0, use this workaround (or: 'Right(Type<String>(v), 5)')
Sleep
Public:
Declare Constructor (ByVal pz As Const ZString Ptr = 0)
Declare Operator Cast () ByRef As ZString
Declare Operator Let (ByVal pz As Const ZString Ptr)
Declare Operator [] (ByVal index As Integer) ByRef As UByte
Declare Destructor ()
Private:
Dim As ZString Ptr p
Dim As UInteger l
End Type
Constructor vZstring (ByVal pz As Const ZString Ptr = 0)
This.l = Len(*pz)
This.p = CAllocate(This.l + 1, SizeOf(ZString))
*This.p = *pz
End Constructor
Operator vZstring.Cast () ByRef As ZString
Return *This.p
End Operator
Operator vZstring.Let (ByVal pz As Const ZString Ptr)
If This.l < Len(*pz) Then
Deallocate(This.p)
This.l = Len(*pz)
This.p = CAllocate(This.l + 1, SizeOf(ZString))
End If
*This.p = *pz
End Operator
Operator vZstring.[] (ByVal index As Integer) ByRef As UByte
Return This.p[index]
End Operator
Destructor vZstring ()
Deallocate(This.p)
End Destructor
Operator Len (ByRef v As vZstring) As Integer
Return Len(Type<String>(v)) '' found nothing better than this
End Operator '' (or: 'Return Len(Str(v))')
Dim As vZstring v = "FreeBASIC"
Print "'" & v & "'", Len(v)
Dim As ZString * 256 z
z = *StrPtr(v) '' 'error 24: Invalid data types' without 'Extends Zstring'
Print "'" & z & "'", Len(z)
v &= Space(2)
Print "'" & v & "'", Len(v)
RSet v, "FreeBASIC" '' 'error 24: Invalid data types' without 'Extends Zstring'
Print "'" & v & "'", Len(v) '' ('Cast' must return a modifiable reference)
Select Case v '' 'error 24: Invalid data types' without 'Extends Zstring'
Case Type<vZstring>(Trim(v) & " ")
Print "Left justified"
Case Type<vZstring>(" " & Trim(v))
Print "Right justified"
End Select
v[0] = Asc("-")
Print "'" & v & "'", Len(v)
Print "'" & Right(v, 5) & "'" '' since fbc 1.09.0, 'Right' supports types with 'Extends Zstring'
'Print "'" & Right(Str(v), 5) & "'" '' before fbc 1.09.0, use this workaround (or: 'Right(Type<String>(v), 5)')
Sleep
- Before fbc 1.09.0, this promotion was not yet fully Zstring type compatible with the built in functions Val/Valint/Vallng/Valuint/Valunlg and Left/Right.
- Since fbc 1.07.0
Dialect Differences:
- Not available in the -lang qb dialect unless referenced with the alias __Extends __Zstring, but unusable because no member procedure is allowed in this dialect.
Differences from QB:
- New to FreeBASIC
See also:
Back to User Defined Types
