2015/06/29
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By atilaneves Uncategorized

Some little-known reasons why D makes day-to-day development easier

When discussing programming languages, most people focus on the big, sexy features: native compilation; functional programming; concurrency. And it makes sense, for the most part these are the features that distinguish programming languages from one another. But the small, little-known features can make regular day-to-day coding a lot easier.

My favourite language is D, as I’ve mentioned before. But languages aren’t like football teams; I’m not a D fan because my dad is or anything like that, I like writing code in the language because I feel I’m more productive. There are several reasons for that, but today I want to talk about the unsexy little things that help me crank out working code faster.

writeln: yes, it’s basically printf. But it’s actually so much more. In most languages, printing out built-in types is easy. “printf(“%d”, intvar)” in C or “cout << intvar” in C++. But you want to actually print one of your own types… you have to write code. Lots of it. Not so in D, the defaults just work. The only real exception are classes, for which you need to override toString. But idiomatic D code doesn’t use many of those, preferring structs. The other good thing about types being easy to print is that you can paste them in to another D source files and compile it. I’ve had to do that a few times.

enums: other languages have enums, they don’t even look very different in D:

enum MyEnum {
    foo,
    bar,
    baz,
}

So how do they help me more than in other languages? First of all, I’ll refer you back to my writeln point: when you print them out you get their string representation, not a number. Internally they’re really just a number like in C, but you never really have to care or worry.

Secondly, “final switch” makes enums a lot more useful by making sure you deal with every single enumeration. Add another value? Your “final switch” code will break, as it should. For those not following the link, in D a final switch on an enum value means that the code will fail to compile unless all enum values have a case statement.

getopt: Defined in std.getopt, it does the very unsexy task of parsing command-line options, but it does it so well. This is the kind of thing that templates allow you to do. In this code:

 int intopt;
 double doubleopt;
 MyEnum enumopt;
 string[] strings;
 auto optInfo = getopt(
     args,
     "i|int", "Int option", &intopt,
     "d|double", "Double option", &doubleopt,
     "e|enum", "Enum option", &enumopt,
     "s|strings", "string list option", &strings,
     );
 if(optInfo.helpWanted) {
     defaultGetoptPrinter("myapp", optInfo.options);
 }

Will do what you expect it to do, and maybe more. It automatically converts the strings given to the program at run-time to the types of the variables that store them. Even better, look at the -s option. If the program is then called with -s string1 -s string2, it’ll hold those two string values. It really is as easy as it looks.

struct constructors: or the lack thereof. Basically, if you write this:

struct Foo {
    int i;
    string s;
    void func() {} //just so it isn't a POD
}

auto foo = Foo(4, "foo");

It’ll compile and work. You can define struct constructors if you want, but it’s the bog-standard one, you don’t have to.

I’m sure there are other lesser-known features in D that make real life programming easier, but these are the ones I can think of of right now.

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