C++17 cannot beat D surely

[H. S. Teoh via Digitalmars-d]

On Sat, Jun 03, 2017 at 03:00:56PM -0700, Ali Çehreli via Digitalmars-d wrote:
> On 06/03/2017 12:12 PM, Steven Schveighoffer wrote:
> 
> > I'd say this deserves a blog post but it would be too short.
> 
> I made many good friends at C++Now. Some of them know Atila from
> CppCon and other C++ conferences. (Beer involved. :) ) They told me
> Atila would routinely tell them during C++ presentations "This
> wouldn't be a talk at a DConf; it's a language feature in D." :)
[...]

In this case, I'd say "this wouldn't be an article about D; it's a
language feature." :-D

Though I'd say we *could* add meat to the article by explaining what
exactly CTFE is, how it works, and why you could just call the standard
library sort at compile-time and have it Just Work(tm) without having to
jump through hoops.

And perhaps demonstrate how easy it is to do this not just with sort,
but with far more complex things.  In fact, significant chunks of Phobos
are now available at CTFE.  For example, you can call std.format at
compile-time to perform some pretty hairy string formatting and have the
result baked into your executable so that you incur none of the cost of
computing it at runtime.

The best part of all this is, as long as you have already written
runtime code that's CTFE-compatible, you don't have to do anything else
to make it work at compile-time. No messing around with constexpr, no
awkward special syntax, no need to jump through hoops, invoke arcane
black magic, etc.. Just call the code with normal runtime syntax from an
expression whose value needs to be known at compile-time, and the
compiler does the rest of you.

And if you need a particular functionality both at compile-time and
during runtime, there's no need to write it twice in two different
sublanguages. You just write one function once, and call it from both
CTFE and at runtime. It Just Works(tm).

Then we could add the icing on the cake by showing off one of
Andrei's(?) little gems in std.random: a RNG generator that checks *at
compile-time* whether a particular set of RNG parameters would produce a
poor-quality RNG, and abort with a compile-error if so.  Meaning that if
the thing compiles at all, you have a minimum quality guarantee. (This
particular gem is described in detail in TDPL, btw, and is one of the
things about D that blew me away when I first read it.)


T

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