[fpc-pascal] Assign() vs AssignTo()

[Martin Schreiber]

On Thursday 11 February 2016 16:13:22 Graeme Geldenhuys wrote:
> Hi,
>
> In TPersistent, we have two virtual methods. Assign() which calls
> AssignTo().
>
> 1) Why are they both virtual? It seems like Assign() is what I call a
> template method, farming its work out to other helper methods - in this
> case, AssignTo(). Normally template methods are not virtual, but their
> helper methods (the ones doing the actual work) are. So again, why is
> Assign() virtual?
>
If one wants to transfer property values from "source" to "dest" one 
calls "dest.assign(source)". If "dest" does not know how to handle "source" 
it calls "source.assignto(self)".

> 2) Now seeing that both are virtual, and that is probably not going to
> change in the RTL, which method is the preferred method to override so
> you have the ability to do MyObject.Assign(MySource)? I've been
> overriding Assign(), but thinking that maybe I should have overridden
> AssignTo() instead.
>
It depends on what knows to handle what. Sometimes both have to be overridden.

Martin