Operator Let (Assign)
Indicates the assignment operator when overloading Operator = (Assignment)
Syntax
`
{ Type | Class | Union } typename
Declare Operator Let ( [ ByRef | ByVal ] rhs As datatype )
End { Type | Class | Union }
Operator typename.Let ( [ ByRef | ByVal ] rhs As datatype )
`
Usage
`
lhs = rhs
`or`
`
lhs => rhs
Parameters
`typename`
name of the `Type`, `Class`, or `Union`.
`lhs`
The variable to assign to.
`rhs`
The value to assign.
Description
`Let` is used to overload the `Operator =[>] (Assignment)` operator and to distinguish it from the comparison operator `Operator = (Equal)`.
`lhs =[>] rhs` will assign the `rhs` to `lhs` by invoking the `Let` operator procedure defined in `typename`.
This includes the case of an object returned from a function by value, by using `Function =[>] rhs` (or `function_identifier =[>] rhs`) assignment.
An operator `Let` (assign) must be defined if the shallow implicit copy is not sufficient. This happens in cases when the object manages dynamically allocated memory or other resources which need to be specially copied (for example if a member pointer points to dynamically allocated memory, the implicit assignment operator will simply copy the pointer value instead of allocate memory and then perform the copy of data).
Note: It is safe to do a check for self-assignment at the top of the `Let` body (by comparing the address of implicit 'this' instance with the address of 'rhs' parameter) to avoid object destruction if previously allocated memory is first deallocated (see example below).
When the operator `Let` (assign) is defined for copy assignment, its parameter (the object to clone) can not be passed by value.
Example
`
Type UDT
Public:
Declare Constructor (ByVal zp As Const ZString Ptr) ''constructor with string initializer
Declare Operator Let (ByRef rhs As UDT) ''operator Let (assignment)
Declare Function getString () As String ''function to get string
Declare Destructor () ''destructor
Private:
Dim zp As ZString Ptr ''private pointer to avoid direct access
End Type
Constructor UDT (ByVal zp As Const ZString Ptr)
This.zp = CAllocate(Len(*zp) + 1)
*This.zp = *zp
End Constructor
Operator UDT.Let (ByRef rhs As UDT)
If @This <> @rhs Then '' check for self-assignment to avoid object destruction
Deallocate(This.zp)
This.zp = CAllocate(Len(*rhs.zp) + 1)
*This.zp = *rhs.zp
End If
End Operator
Function UDT.getString () As String
Return *This.zp
End Function
Destructor UDT ()
Deallocate(This.zp)
End Destructor
Dim u As UDT = UDT("")
u = Type<UDT>("Thanks to the overloading operator Let (assign)")
Print u.getString
Sleep
`
Output:

    Thanks to the overloading operator Let (assign)

Version

- Before fbc version 1.20.0, assigning one array was not supported.

Dialect Differences

- In the -lang qb and -lang fblite dialects, this operator cannot be overloaded.
- In the -lang qb and -lang fblite dialects, an assignment expression can be preceded by the `Let` keyword.

Differences from QB

- None.

See also

- `Let`
- `Operator Let() (Assignment)`
- `Operator =[>] (Assignment)`
- `Operator = (Equal)`
- Coercion and Conversion