Re: Blogpost about the T.init problem
On Wednesday, 11 July 2018 at 16:58:53 UTC, Greatsam4sure wrote: On Tuesday, 10 July 2018 at 13:41:56 UTC, FeepingCreature wrote: [...] Every language is plague with one bug or the order. For those will great love for the language they lend a helping hand to fixed the bug. I expect you to help also in whatsoever capacity you can. What do you think pull requests are? I am just learning D but I am thoroughly satisfy with the language. For me it is truly joy. Goody for you, but how does that help?
Re: Blogpost about the T.init problem
On Wednesday, 11 July 2018 at 07:30:59 UTC, FeepingCreature wrote:
On Tuesday, 10 July 2018 at 21:08:32 UTC, Cym13 wrote:
First of all I must point that I would very much like to have
seen a code actually producing an error in that article.
Contrary to what is hinted just taking the struct and putting
using it with Nullable or format() caused no error for me and
worked as expected.
To reproduce the format issue, try to print the struct with
writefln!"%s"(MyDomainType()).
To reproduce the Nullable issue, you need to slightly modify
the struct. In Phobos, Nullable will (due to an abundance of
caution) refuse to initialize the struct if the default
constructor is disabled; also you need a destructor. However,
for this it is enough to use any type that has a destructor, so
that an implicit struct destructor is generated. For verbosity,
I'll write it out:
struct MyDomainData {
string username;
this(string username) @safe
in(!username.empty) // only non-empty usernames please!
do { this.username = username; }
// let's formalise the restriction.
invariant { assert(!username.empty); }
string toString() { return null; }
~this() @safe { }
}
Then just stick it in a Nullable. No explicit .init needed.
That said, I may be missing something obvious but what
prevents you from overloading the init field?
struct MyDomainData {
string username;
@disable this(); // don't make a MyDomainData() by
accident!
this(string username)
in(!username.empty) // only non-empty usernames please!
do { this.username = username; }
// let's formalise the restriction.
invariant { assert(!username.empty); }
string toString() { ... }
static @property MyDomainData init() {
return MyDomainData("uninitialized");
}
...
}
auto test = MyDomainData.init; // There, no error
Of course that value means nothing but .init isn't meant to
actually mean something anyway, it's just a valid value and
that's what that init is proposing, so it shouldn't cause any
more bugs than empty .init in a normal case.
That would work, it's just a really horrible hack and I hate
it. We're constructing a fictitious domain value that passes
our invariants while having zero correspondence to the real
world, *just to pass our invariants*. It's an obvious sign of a
language issue.
If so, then the only language solution is to remove either
invariants or .init, because as long as .init can be called but
cannot be made to conform to your invariant, then your design is
beyond the scope of the language and you're in a pickle.
But the fact is that it's not a language issue and there are
several ways in user code to guarantee that .init satisfies the
invariant. In fact that very statement suggests a solution that
Timothy Cour suggested earlier:
invariant {
if(this is typeof(this).init) return;
assert(!username.empty);
}
Re: Blogpost about the T.init problem
On Wednesday, 11 July 2018 at 16:54:18 UTC, Greatsam4sure wrote: On Tuesday, 10 July 2018 at 13:41:56 UTC, FeepingCreature wrote: [...] Sincerely speaking D language does not merit all these criticism. The magnitude of criticism on D language does not really make sense to me. I am yet to see a language so user friendly as D with such power and strength.I trust one day the world will see and know that D is a language build for programmers for great productivity and not just another money making machine Yeah, D is great so let's not even have a bug database, eh?
Re: On D in competitive programming
On Saturday, 28 July 2018 at 21:33:04 UTC, Ivan Kazmenko wrote: [snip] 2. When you briefly explain templates I think it's important to mention that empty parentheses may be omitted to allow the reader to make the link between function!(arg1)(arg2) and map!something. Explaining UFCS isn't necessary there though I think since it's obvious that there is some kind of chaining at play (not that you did, just thinking out loud). Yeah, good point, mentioned it now. Actually, map!something does not drop empty parentheses, so mentioning that does not help. Parentheses containing 0 or 1 arguments can be omitted ... and you omit them for 1 argument in 3 places, and no instances of omitted empty parentheses. And I think it would be less confusing to an unfamiliar reader to mention UFCS, because the chained calls don't fit the function !(args1) (args2) syntax that you mention. [snip]
Re: Argon: an alternative parser for command-line arguments
On Thursday, 3 March 2016 at 09:33:38 UTC, Johannes Pfau wrote: Am Thu, 03 Mar 2016 09:09:38 + schrieb Markus Laker : * It can open files specified at the command line. It can do a simplified version of what cat(1) does and many Perl programs so, and open a file specified by the user or fall back to reading from stdin. There's also a convention that the user can type "-" to mean stdin or stdout, depending on the open-mode you specify. The rest of this list sounds quite good, but please reconsider automatically opening files: https://media.ccc.de/v/32c3-7130-the_perl_jam_2 No one wants to watch a 40 minute video just to find out what your point is. I guess the scenario can't happen in D as our open file methods won't execute programs (!) but still But still? What other problem is there? What does it matter whether the command line parser opens the file or some other part of the program does?
