Dimensional Data

What is a Custom Managed Record in Delphi? Records in Delphi can have fields of any data type. When a record has plain (non-managed) fields, like numeric or other enumerated values there isn’t much to do for the compiler. Creating and disposing the record consists of allocating memory or getting rid of the memory location. (Notice that by default Delphi does not zero-initialize records.) If a record has a field of a type managed by the compiler (like a string or an interface), the compiler needs to inject extra code to manage the initialization or finalization. A string, for example, is reference counted so when the record goes out of scope the string inside the record needs to have its reference count decreased, which might lead to de-allocating the memory for the string. Therefore, when you are using such a managed record in a section of the code, the compiler automatically adds a try-finally block around that code, and makes sure the data is cleared even in case of an exception. This has been the case for a long time. In other words, managed records have been part of the Delphi language. Records with Initialize and Finalize Operators  Now in Delphi 10.4 record type supports custom initialization and finalization, beyond the default operations the compiler does for managed records. You can declare a record with custom initialization and finalization code regardless of the data type of its fields, and you can write such custom initialization and finalization code. This is achieved by adding specific, new operators to the record type (you can have one without the other if you want).Below is a simple code snippet: type TMyRecord = record Value: Integer; class operator Initialize (out Dest: TMyRecord); class operator Finalize(var Dest: TMyRecord); end; You need to write the code for the two class methods, of course, for example logging their execution or initializing the record value — here we are also logging a reference to memory location, to see which record is performing each individual operation: class operator TMyRecord.Initialize (out Dest: TMyRecord); begin Dest.Value := 10; Log(‘created’ + IntToHex (Integer(Pointer(@Dest))))); end; class operator TMyRecord.Finalize(var Dest: TMyRecord); begin Log(‘destroyed’ + IntToHex (Integer(Pointer(@Dest))))); end; The huge difference between this construction mechanism and what was previously available for records is the automatic invocation. If you write something like the code below, you can invoke both the initializer and the finalizer, and end up with a try-finally block generated by the compiler for your managed record instance. procedure LocalVarTest; var my1: TMyRecord; begin Log (my1.Value.ToString); end; With this code you’ll get a log like: created 0019F2A8 10 destroyed 0019F2A8 Another scenario is the use of inline variables, like in: begin var t: TMyRecord; Log(t.Value.ToString); which gets you the same sequence in the log.  The Assign Operator The := assignment flatly copies all of the data of the record fields. While this is a reasonable default, when you have custom data fields and custom initialization you might want to change this behavior. This is why for Custom Managed Records you can also define an assignment operator. The new operator is invoked with the := syntax, but defined as Assign: class operator Assign (var Dest: TMyRecord; const [ref] Src: TMyRecord); The operator definition must follow very precise rules, including having the first parameter as a reference […]