Revision [21690]
This is an old revision of KeyPgTypeAlias made by fxm on 2016-11-09 15:47:15.
Type (Alias)
Declares an alternative name for a type
Syntax:
Type typename as symbol
Parameters:
typename
new alternative name.
symbol
symbol or data type declaration to associate with typename.
Description:
symbol may refer to any declared data type including a built-in data type, Sub or Function pointer, Type declaration, Union declaration, or Enum declaration.
A type alias can be used to allow forward declarations of parameters in procedure declarations, but only used with pointers or parameters passed by reference (excluding arrays). Generally the bodies of such procedures need to be implemented further in the code once the actual types are well defined.
A type alias can also be used to allow forward declarations of data fields in User Defined Types, but only used with pointers.
A type alias must be used to allow declaration of pointer to a function pointer, otherwise ptr applies on return type and not on function.
A type alias can be used to allow forward declarations of parameters in procedure declarations, but only used with pointers or parameters passed by reference (excluding arrays). Generally the bodies of such procedures need to be implemented further in the code once the actual types are well defined.
A type alias can also be used to allow forward declarations of data fields in User Defined Types, but only used with pointers.
A type alias must be used to allow declaration of pointer to a function pointer, otherwise ptr applies on return type and not on function.
Examples:
Type ParentFwd As Parent
Type Child
Name As ZString * 32
ParentRef As ParentFwd Ptr
''...
End Type
Type Parent
Name As ZString * 32
ChildList(0 To 9) As Child
''...
End Type
Dim p As Parent
p.Name = "Foo"
With p.ChildList(0)
.Name = "Jr."
.ParentRef = @p
'' ...
End With
With p.ChildList(0)
Print .Name; " is child of "; .parentRef->Name
End With
Type Child
Name As ZString * 32
ParentRef As ParentFwd Ptr
''...
End Type
Type Parent
Name As ZString * 32
ChildList(0 To 9) As Child
''...
End Type
Dim p As Parent
p.Name = "Foo"
With p.ChildList(0)
.Name = "Jr."
.ParentRef = @p
'' ...
End With
With p.ChildList(0)
Print .Name; " is child of "; .parentRef->Name
End With
Function triple (ByVal i As Integer) As Integer
Return 3 * i
End Function
Type As Function (ByVal As Integer) As Integer function_alias
'Dim As Function (Byval As Integer) As Integer f = @triple '' this syntax works but is less readable than the next line
Dim As function_alias f = @triple
Print f(123)
'Dim As Function (Byval As Integer) As Integer Ptr pf = @f '' this syntax does not work because Ptr applies on Integer and not on function
Dim As function_alias Ptr pf = @f '' this syntax works
Print (*pf)(123) '' the dereferenced pointer to procedure pointer must be surrounded by parenthesis
Return 3 * i
End Function
Type As Function (ByVal As Integer) As Integer function_alias
'Dim As Function (Byval As Integer) As Integer f = @triple '' this syntax works but is less readable than the next line
Dim As function_alias f = @triple
Print f(123)
'Dim As Function (Byval As Integer) As Integer Ptr pf = @f '' this syntax does not work because Ptr applies on Integer and not on function
Dim As function_alias Ptr pf = @f '' this syntax works
Print (*pf)(123) '' the dereferenced pointer to procedure pointer must be surrounded by parenthesis
Differences from QB:
- New to FreeBASIC
See also:
Back to User Defined Types
