REM Sacado del forum de FreeBASIC (https://www.freebasic.net/forum/viewtopic.php?t=20432)

Type singleton
    Public :
    Declare Static Function crearInstancia() As singleton Ptr
    Declare Destructor ()
    Dim i As Integer
    Private :
    Declare Constructor()
    Declare Constructor(Byref rhs As singleton)
    Declare Static Function instancia(Byval crear As Integer) As singleton Ptr
End Type

Static Function singleton.crearInstancia() As singleton Ptr
    Return singleton.instancia(1)
End Function

Static Function singleton.instancia(Byval crear As Integer) As singleton Ptr
    Static ref As singleton Ptr = 0
    Function = 0
    If crear = 0 Then
        ref = 0
    Elseif ref = 0 Then
        ref = New singleton
        Function = ref
    End If
End Function

Constructor singleton ()
End Constructor

Destructor singleton()
singleton.instancia(0)
End Destructor

'-----------------------------------------------------------------------------
Dim As singleton Ptr ps1 = singleton.crearinstancia()
ps1->i = 1234
Print ps1, ps1->i

Dim As singleton Ptr ps2 = singleton.crearinstancia()
Print ps2

Delete ps1

Dim As singleton Ptr ps3 = singleton.crearinstancia()
Print ps3, ps3->i
Delete ps3
Sleep