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 (whatever their passing mode), or otherwise with parameters (excluding arrays) but passed or returned only by reference. Generally the bodies of such procedures need to be implemented further in the code once the actual types are well defined (for example because of the passing of such a reference; or when such a pointer passed is then dereferenced in any form).
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 declaration can also be nested inside a UDT structure declaration for a `Type or a` Union.
Example
`
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
`
`
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 ''this syntax works but is less readable than the next code line
Dim As function_alias f
f = @triple
Print f(123)
'Dim As Function (Byval As Integer) As Integer Ptr pf ''this syntax does not work because Ptr applies on Integer and not on function
Dim As function_alias Ptr pf ''this syntax works
pf = @f
Print (*pf)(123) ''the dereferenced pointer to procedure pointer must be enclosed in parentheses
`
Version

- Since fbc 1.10.0: Nesting of a Type Alias declaration inside a structure declaring a UDT (Type or Union) is allowed.

Differences from QB

- New to FreeBASIC

See also

- `Type...End Type`
- `Type (Temporary)`