Tips for golfing in D2

Question

What general tips do you have for golfing in D? I'm looking for ideas that can be applied to code golf problems in general that are at least somewhat specific to D (e.g. "remove comments" is not an answer). Please post one tip per answer.

Adalynn · Accepted Answer · 2016-12-27 18:35:41Z

Look, no parens!

D's functions and template functions can be called as values, methods (won't help), and properties.

I can't believe no one has said this yet. I'll list the ones that save bytes:

fun() and fun!()() shorten to fun (assuming there is no variable fun).
fun(par) shortens to par.fun (assuming par has no property/method fun, as well as par not being an expression like 5+2).
fun!(T)() shortens to fun!T
fun!(T)(par) shortens to par.fun!T (assuming par has no property/method fun)

And with objects:

new cls() shortens to new cls (More JavaScript anyone?)
obj.fun() and obj.fun!()() shorten to obj.fun
obj.fun!(T)() shortens to obj.fun!T

One final thing, use old versions. It allows you to use deprecated features that shorten your code. That said, best advice: D isn't good for code-golf. It is a great language, just not for code-golf.

\$\begingroup\$ Accepting for now :) \$\endgroup\$

cat
– cat

2016-12-27 16:56:59 +00:00
Commented Dec 27, 2016 at 16:56 — cat
– cat, Commented Dec 27, 2016 at 16:56
\$\begingroup\$ Yeah, good to know there's still fans of D here. \$\endgroup\$

Adalynn
– Adalynn

2016-12-27 22:38:49 +00:00
Commented Dec 27, 2016 at 22:38 — Adalynn
– Adalynn, Commented Dec 27, 2016 at 22:38

cat · Accepted Answer · 2016-03-10 00:10:01Z

D is JavaScript.

Obviously not. But, when dealing with float, double and real, nan is a value which must be handled, and, as specified by IEEE 754, NaN does not compare equal with itself.

writeln(double.nan == double.nan); // false

Meaning,

writeln(value!=value); // only true for nan

is way shorter than

import std.math; writeln(isNaN(value));

Obviously, always use math.isNaN for real code. ;)

cat · Accepted Answer · 2016-02-27 23:14:08Z

1

D has type inference and an auto keyword. If the object is not int, then auto is probably shorter.

answered Feb 27, 2016 at 23:14

cat

6,0502 gold badges27 silver badges45 bronze badges

\$\begingroup\$ Does auto work when building an associative array with the KeyType[ValueType] syntax? \$\endgroup\$

Alex A.
– Alex A.

2016-02-27 23:30:14 +00:00
Commented Feb 27, 2016 at 23:30
\$\begingroup\$ @AlexA. auto asd = ["a":1, "b": 2]; works, but since KeyType[ValueType] would go in the place of the auto keyword, I don't know if that will always work with types for which literals can't be constructed \$\endgroup\$

cat
– cat

2016-02-27 23:39:03 +00:00
Commented Feb 27, 2016 at 23:39
\$\begingroup\$ @AlexA. auto arr = ["a": true, "b": 6]; works, the keys and values must be of compatible types \$\endgroup\$

cat
– cat

2016-02-28 16:43:58 +00:00
Commented Feb 28, 2016 at 16:43

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Community · Accepted Answer · 2017-04-13 12:39:08Z

D is great at method chaining, but:

str.toLower.strip().split("").sort();

is the same as

sort(split(strip(str.toLower),""));

and usually the non-chained one is shorter, which I just realised, which lets me shorten my answer to Manage Trash So :D

\$\begingroup\$ It's those dots \$\endgroup\$

CalculatorFeline
– CalculatorFeline

2016-02-28 01:25:51 +00:00
Commented Feb 28, 2016 at 1:25 — CalculatorFeline
– CalculatorFeline, Commented Feb 28, 2016 at 1:25

cat · Accepted Answer · 2016-02-28 00:36:22Z

D, as a multiparadigm (Object Functional) systems programming language, seems to embrace TIMTOWTDI, or There Is More Than One Way To Do It.

Case in point, writing the program's argv:

import std.stdio, std.array, std.algorithm; void main(string[] args) { for(int i=0;i<args.length;writeln(args[i++])){}; foreach(a;args)writeln(a); each!writeln(args); }

Note the C-style for-loop requires {} as the empty block and will not accept a semicolon or nothing as a blank statement, in this case. Usually, or ; are no-ops.

@AlexA. function D main parameters must be main() or main(string[] args) moreover, char is literally one character, char* is a pointer to literally one character and char[] is an array of character literals (strings are different). D != C || C++ — cat
– cat, Commented Feb 28, 2016 at 1:40

cat · Accepted Answer · 2016-02-28 14:27:59Z

1

D has a few types of C#-style lambda expressions, which can be assigned and stand alone:

(int a,int b)=>a*b; auto a=(int a,int b)=>a*b;

However, unlike C#, the signature's types are still needed because D doesn't have Haskell-level type inferencing.

https://dlang.org/spec/expression.html#Lambda

answered Feb 28, 2016 at 14:27

cat

6,0502 gold badges27 silver badges45 bronze badges

\$\begingroup\$ Function templates for golfing the types? T f(T)(T a,T b){return a + b} should infer T as int in f(5); \$\endgroup\$

fede s.
– fede s.

2016-05-05 19:35:29 +00:00
Commented May 5, 2016 at 19:35
\$\begingroup\$ @fedes. Hello, friend! Yes, you are exactly correct (but I think/hope "untyped" lambdas will be shorter than typed function expressions). \$\endgroup\$

cat
– cat

2016-05-05 19:48:39 +00:00
Commented May 5, 2016 at 19:48
\$\begingroup\$ Ah, ofc! When I decide to take yet another look on D, who do I find? :D I objectively declare you have good taste on languages \$\endgroup\$

fede s.
– fede s.

2016-05-05 19:52:44 +00:00
Commented May 5, 2016 at 19:52
\$\begingroup\$ @fedes. Aw, why thank you! :P that implies you do too (but I haven't spent enough time in front of Smalltalk, yet anyways :) ) \$\endgroup\$

cat
– cat

2016-05-05 20:01:30 +00:00
Commented May 5, 2016 at 20:01

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cat · Accepted Answer · 2016-05-05 20:00:42Z

If the question requires a full program, the module declaration is surprisingly unnecessary.

*cough* Java, anyone? *clears throat* Actually, D's module system is older than Java's.

cat · Accepted Answer · 2016-02-28 00:13:02Z

0

Like C/C++, main can be int or void, but void main(){} will always be shorter than int main(){return my_func_returning_int;}.

answered Feb 28, 2016 at 0:13

cat

6,0502 gold badges27 silver badges45 bronze badges

\$\begingroup\$ If the question ask to output an integer wouldn't int main(){return output} be shorter? \$\endgroup\$

Andreas Louv
– Andreas Louv

2016-02-28 01:44:28 +00:00
Commented Feb 28, 2016 at 1:44
\$\begingroup\$ @dev-null if the question asks for a full program writing an integer to stdout then import std.stdio;void main(){write(7);} is what's needed. I doubt a question would mandate the program return a number because many languages can't set return codes \$\endgroup\$

cat
– cat

2016-02-28 01:45:07 +00:00
Commented Feb 28, 2016 at 1:45
\$\begingroup\$ @dev-null however, yes, in that case that it should not be written to stdout but returned, it would be shorter \$\endgroup\$

cat
– cat

2016-02-28 01:45:40 +00:00
Commented Feb 28, 2016 at 1:45
3

\$\begingroup\$ Usually you are allowed to return / output the most convenient way for your language. But I guess D only support exit codes from 0-255? \$\endgroup\$

Andreas Louv
– Andreas Louv

2016-02-28 01:48:08 +00:00
Commented Feb 28, 2016 at 1:48
\$\begingroup\$ @dev-null actually, POSIX only supports exit codes up to 255. I don't know about Windows, but on Unix / Linux an exit code over 255 wraps around, because of overflow. \$\endgroup\$

cat
– cat

2016-02-28 01:50:23 +00:00
Commented Feb 28, 2016 at 1:50

Add a comment |

cat · Accepted Answer · 2016-03-03 00:16:54Z

Calling a function on an object with no other arguments

reverse(x);

can nearly always be shortened to

x.reverse;

to shave a byte or more.

This is because the . makes the LHS an implicit first argument, and templating lets us choose the right function for the args.

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