sumtypes for D

[H. S. Teoh]

On Wed, Nov 30, 2022 at 12:42:38AM +0000, deadalnix via Digitalmars-d wrote:
> On Wednesday, 30 November 2022 at 00:10:47 UTC, H. S. Teoh wrote:
[...]
> > +1, I think this is a better approach.  If a library type can't do
> > what a built-in type does, then extend the language until it can.
> > As Andrei said in TDPL: "experience has shown time and again that
> > offering many magic types that are unattainable to user code is a
> > frustrating proposition and a sign of poor language design" [TDPL,
> > 2010 ed, p.239].
[...]
> Damn, this Andrei guy, he knew one thing or two...

And to elaborate a little, for those people who groan at "yet another
library type": a common objection is that a library type has poorer
error messages.  Well, it's just the same thing in different clothes: if
a library type can't have good error messages, why is that?  Because the
language cannot express certain things, or can't do it well, so the
library author's hands are tied.  Giving up and pushing the type into
the language is merely avoiding the problem (now the compiler writer has
to solve the same problems, only in the compiler -- the amount of effort
required is equivalent).  What actually addresses the problem is: fix
the language so that the library author *can* provide good error
messages.

Because this isn't just about adding sumtype or whatever other magic
type, this is about making it possible for *any* user type to provide
the same level of functionality as built-in types.  It's about
empowering the library writer so that he can replicate the power of a
built-in type, integrated so well into the language that it feels like
native type.  This includes containers that behave like built-in arrays,
ARC'd types that behave like pointers, etc..  Solve this at the core,
and it will enable progress on many other fronts.  Fail at this, and
you're doomed to putting out individual fires one by one, ala
whack-a-mole.  Today it's sumtypes, tomorrow it's ARC types, the next
day it's head-immutable, it will never end.


T

-- 
Don't drink and derive. Alcohol and algebra don't mix.