[PATCH] Introduce a section to the programmers manual about type hierarchies, polymorphism, and virtual dispatch.

[Duncan P. N. Exon Smith]

Chandler: nice writeup.

> On 2015 Jan 27, at 04:11, Sean Silva <chisophugis at gmail.com> wrote:
> 
> ================
> Comment at: docs/ProgrammersManual.rst:2538-2539
> @@ +2537,4 @@
> +
> +If you do need to introduce a type hierarchy, we often prefer to use explicitly
> +closed type hierarchies with manual tagged dispatch rather than the open
> +inheritance model and virtual dispatch that is more common in C++ code. This is
> ----------------
> Probably want a link to http://llvm.org/docs/HowToSetUpLLVMStyleRTTI.html .

I second this.  Neatly clears up unfamiliarity with the terms.

> You may want to use the catch-phrase "LLVM-style RTTI" somewhere here as well.
> 
> Also feel free to make changes to HowToSetUpLLVMStyleRTTI to better fit into the context of the discussion you're adding here.