New and Delete


The different operators New (Implicit/Overload/Expression/Placement) and Delete (Implicit/Overload/Statement), and all their array-versions New[] and Delete[]

Definition
There may be confusion in the user mind between the different operators New and Delete (despite the documentation that distinguishes them from each other through some different pages):
  • 'Operator New Implicit' (inaccessible by user):
  • - It is a static function that only allocates memory (it is not very different from Allocate).
  • Operator New Overload:
  • - It is a member operator (static function) that can overload the 'Operator New Implicit' only for user-defined types.
    - So the user can define its own dynamic memory allocation process part (the following process part for implicit data construction can not be modified).
  • 'Operator Delete Implicit' (inaccessible by user):
  • - It is a static sub that only frees the memory (it is not very different from Deallocate).
  • Operator Delete Overload:
  • - It is a member operator (static sub) that can overload the 'Operator Delete Implicit' only for user-defined types.
    - So the user can define its own memory deallocation process part (the previous process part for implicit data destruction can not be modified).
  • Operator New Expression:
  • - It starts by using the 'Operator New Implicit/Overload' (the implicit, or the overload if exists) to allocate memory.
    - Then it invokes the constructor for the right type of object. If that object contains any other objects (either embedded or as base types) those constructors as invoked as well.
    - So the final result is memory allocated and object constructed.
    - This operator applies to pre-defined types (except fixed-length strings) as well as user-defined types.
  • Operator Delete Statement:
  • - It starts by invoking the destructor for the right type of object. If that object contains any other objects (either embedded or as base types) those destructors as invoked as well.
    - Then it uses the 'Operator Delete Implicit/Overload' (the implicit, or the overload if exists) to deallocate memory.
    - So the final result is object destroyed and memory freed.
    - This operator applies to pre-defined types (except fixed-length strings) as well as user-defined types.
  • Operator Placement New:
  • - It only constructs object at a specified memory address (already allocated). This operator applies to pre-defined types (except fixed-length strings) as well as user-defined types.

Similar definition for 'Operator New[] Implicit/Overload/Expression', 'Operator Delete[] Implicit/Overload/Statement' and 'Operator Placement New[]', which are only the (one-dimensional) array-versions of the previous operators (there is construction/destruction loop on the array elements).

Instances created with 'Operator New Overload/Expression' must be freed with 'Operator Delete Overload/Statement'.
Instance array created with 'Operator New[] Overload/Expression' must be freed with 'Operator Delete[] Overload/Statement', the array-version of 'Operator Delete Overload/Statement'.
User can not mix and match the different versions of the operators.

Instances constructed at a specified memory address with 'Operator Placement New' must never induce a symmetric freeing with any 'Operator Delete' on the address (because the memory has been allocated in another way than by the 'Operator Placement New').
Instance array constructed at a specified memory address with 'Operator Placement New[]' must never induce a symmetric freeing with any 'Operator Delete[]' on the address (because the memory has been allocated in another way than by the 'Operator Placement New[]').
For such UDT instances, the proper way to just destroy each instance if necessary, is to call only the destructor if one exists (implicitly or explicitly), with syntax as for a member method by using member access operator.

Note: Any operators 'New[]' or 'Delete[]' (the array versions for statement/expression/overload operators) and even the overload operator 'Delete' are not directly compatible with inheritance polymorphism, because the use of a sub-type pointer (instead of the real type) mainly fails for accessing the other elements (except the first).

Algorithm (applied to user-defined types)
Operator New/New[] Expression:
'       OPERATOR NEW/NEW[] EXPRESSION
'                     V
'                     |
'              call if there is >----------------------------.
'                   else                                     :
'                     v                                      v
'       (Operator New/New[] Implicit)          (Operator New/New[] Overload)
'                     :                                      :
'          BASIC MEMORY ALLOCATION            USER BODY for memory allocation
'                     :                                      :
'                     :<-------------------------------------'
'                     |
'                     |<-------------------------------------.
'                     |                                      :
'        DATA FIELDS INITIALIZATION                          :
'        OBJECT FIELDS CONSTRUCTION                          :
'           (VPTR INITIALIZATION)                            :
'                     |                                      :
'              call if there is >-----------.                :
'                   else                    :                :
'                     v                     v                :
'                     :            (User Constructor)        :
'                     :                     :                :
'                     :                 USER BODY            :
'                     :                     :                :
'                     :<--------------------'                :
'                     |                                      :
'        loop if array-version NEW[] >-----------------------'
'                   else
'                     v
'                     |
'                     V

Operator Delete/Delete[] Statement:
'     OPERATOR DELETE/DELETE[] STATEMENT
'                     V
'                     |
'                     |<-------------------------------------.
'                     |                                      :
'          (VPTR REINITIALIZATION)                           :
'                     |                                      :
'              call if there is >-----------.                :
'                   else                    :                :
'                     v                     v                :
'                     :             (User Destructor)        :
'                     :                     :                :
'                     :                 USER BODY            :
'                     :                     :                :
'                     :<--------------------'                :
'                     |                                      :
'         OBJECT FIELDS DESTRUCTION                          :
'                     |                                      :
'       loop if array-version DELETE[] >---------------------'
'                   else
'                     v
'                     |
'              call if there is >----------------------------.
'                   else                                     :
'                     v                                      v
'    (Operator Delete/Delete[] Implicit)    (Operator Delete/Delete[] Overload)
'                     :                                      :
'         BASIC MEMORY DEALLOCATION          USER BODY for memory deallocation
'                     :                                      :
'                     :<-------------------------------------'
'                     |
'                     V

Operator Placement New/New[]:
'        OPERATOR PLACEMENT NEW/NEW[]
'                     V
'                     |
'                     |<-------------------------------------.
'                     |                                      :
'        DATA FIELDS INITIALIZATION                          :
'        OBJECT FIELDS CONSTRUCTION                          :
'           (VPTR INITIALIZATION)                            :
'                     |                                      :
'              call if there is >-----------.                :
'                   else                    :                :
'                     v                     v                :
'                     :             (User Constructor)       :
'                     :                     :                :
'                     :                 USER BODY            :
'                     :                     :                :
'                     :<--------------------'                :
'                     |                                      :
'        loop if array-version NEW[] >-----------------------'
'                   else
'                     v
'                     |
'                     V

Example
Example that uses the operators New (Overload/Expression/Placement) and Delete (Overload/Statement), and all their array-versions New[] and Delete[]:
(all the 10 operators New and Delete accessible by the user):
Declare Sub printArray (ByRef label As String = "", array() As String)


Type UDT
    Declare Constructor ()
    Declare Destructor ()
    Declare Operator New (ByVal size As UInteger) As Any Ptr    ' Operator New Overload
    Declare Operator New[] (ByVal size As UInteger) As Any Ptr  ' Operator New[] Overload
    Declare Operator Delete (ByVal buf As Any Ptr)              ' Operator Delete Overload
    Declare Operator Delete[] (ByVal buf As Any Ptr)            ' Operator Delete[] Overload
    Dim As String array (1 To 4)
End Type

Constructor UDT ()
    Static As Integer n
    Print "    Constructor"
    printArray("        init: @" & @This & " (descriptors) -> ", This.array())
    For i As Integer = LBound(This.array) To UBound(This.array)
        This.array(i) = Chr(Asc("a") + n + i - LBound(This.array))
    Next i
    printArray(" => ", This.array())
    Print
    n += UBound(This.array)- LBound(This.array) + 1
End Constructor

Destructor UDT ()
    Print "    Destructor"
    printArray("        erase: @" & @This & " (descriptors) -> ", This.array())
    Erase This.array
    printArray(" => ", This.array())
    Print
End Destructor

Operator UDT.New (ByVal size As UInteger) As Any Ptr
    Print "    Operator New Overload"
    Dim As Any Ptr p = Allocate(size)                   ' Memory allocation (with passed size)
    Print "        memory allocation: ";
    Print size & " Bytes from @" & p
    Return p                                            ' Returning memory pointer
End Operator

Operator UDT.New[] (ByVal size As UInteger) As Any Ptr
    Print "    Operator New[] Overload"
    Dim As Any Ptr p = Allocate(size)                   ' Memory allocation (with passed size)
    Print "        memory allocation: ";
    Print size & " Bytes from @" & p
    Return p                                            ' Returning memory pointer
End Operator

Operator UDT.Delete (ByVal buf As Any Ptr)
    Print "    Operator Delete Overload"
    Deallocate(buf)                                     ' Memory deallocation (with passed pointer)
    Print "        memory deallocation: ";
    Print "for @" & buf
End Operator

Operator UDT.Delete[] (ByVal buf As Any Ptr)
    Print "    Operator Delete[] Overload"
    Deallocate(buf)                                     ' Memory deallocation (with passed pointer)
    Print "        memory deallocation: ";
    Print "for @" & buf
End Operator


Print "Operator New Expression"
Dim As UDT Ptr pu1 = New UDT         ' Operator New Expression
Print "Operator Delete Statement"
Delete pu1                           ' Operator Delete Statement
Sleep

Print
Print "Operator New[] Expression"      
Dim As UDT Ptr pu2 = New UDT[2]      ' Operator New[] Expression
Print "Operator Delete[] Statement"
Delete[] pu2                         ' Operator Delete[] Statement
Sleep

Dim As Byte buffer(1 To 256)
Dim As Any Ptr p = @buffer(1)

Print
Print "Operator Placement New"
Dim As UDT Ptr pu3 = New(p) UDT      ' Operator Placement New
Print "User call of Destructor"
pu3->Destructor()                    ' User Call of Destructor
Sleep

Print
Print "Operator Placement New[]"
Dim As UDT Ptr pu4 = New(p) UDT[2]   ' Operator Placement New[]
For i As Integer = 0 To 1
    Print "User Call of Destructor"
    pu4[i].Destructor()              ' User Call of Destructor
Next i
Sleep


Sub printArray (ByRef label As String = "", array() As String)
    Print label & "{";
    For i As Integer = LBound(array) To UBound(array)
        Print """" & array(i) & """";
        If i < UBound(array) Then
            Print ",";
        End If
    Next I
    Print "}";
End Sub
Output example (for a 64-bit system):
Operator New Expression
	Operator New Overload
		memory allocation: 96 Bytes from @1728352
	Constructor
		init: @1728352 (descriptors) -> {"","","",""} => {"a","b","c","d"}
Operator Delete Statement
	Destructor
		erase: @1728352 (descriptors) -> {"a","b","c","d"} => {"","","",""}
	Operator Delete Overload
		memory deallocation: for @1728352

Operator New[] Expression
	Operator New[] Overload
		memory allocation: 200 Bytes from @1728352
	Constructor
		init: @1728360 (descriptors) -> {"","","",""} => {"e","f","g","h"}
	Constructor
		init: @1728456 (descriptors) -> {"","","",""} => {"i","j","k","l"}
Operator Delete[] Statement
	Destructor
		erase: @1728456 (descriptors) -> {"i","j","k","l"} => {"","","",""}
	Destructor
		erase: @1728360 (descriptors) -> {"e","f","g","h"} => {"","","",""}
	Operator Delete[] Overload
		memory deallocation: for @1728352

Operator Placement New
	Constructor
		init: @1375248 (descriptors) -> {"","","",""} => {"m","n","o","p"}
User call of Destructor
	Destructor
		erase: @1375248 (descriptors) -> {"m","n","o","p"} => {"","","",""}

Operator Placement New[]
	Constructor
		init: @1375248 (descriptors) -> {"","","",""} => {"q","r","s","t"}
	Constructor
		init: @1375344 (descriptors) -> {"","","",""} => {"u","v","w","x"}
User Call of Destructor
	Destructor
		erase: @1375248 (descriptors) -> {"q","r","s","t"} => {"","","",""}
User Call of Destructor
	Destructor
		erase: @1375344 (descriptors) -> {"u","v","w","x"} => {"","","",""}

See also
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