Back in 2017, I wrote about why the D programming language is a great choice for development. But there is one outstanding feature in D I didn't expand enough on: the Universal Function Call Syntax (UFCS). UFCS is a syntactic sugar in D that enables chaining any regular function on a type (string, number, boolean, etc.) like its member function of that type.

If you don't already have D installed, install a D compiler so you can run the D code in this article yourself.

Consider this example code:

// file: ufcs_demo.d



module ufcs_demo;



import std.stdio : writeln;



int[] evenNumbers(int[] numbers)

{

    import std.array : array;

    import std.algorithm : filter;



    return numbers.filter!(n => n % 2 == 0).array;

}



void main()

{

    writeln(evenNumbers([1, 2, 3, 4]));

}

Compile this with your favorite D compiler to see what this simple example application does:

$ dmd ufcs_demo.d

$ ./ufcs_demo

[2, 4]

But with UFCS as a built-in feature of D, you can also write your code in a natural way:

...

writeln([1, 2, 3, 4].evenNumbers());

...

or completely remove the now-redundant parenthesis to make it feel like evenNumbers is a property:

...

writeln([1, 2, 3, 4].evenNumbers); // prints 2, 4

...

So the complete code now becomes:

// file: ufcs_demo.d



module ufcs_demo;



import std.stdio : writeln;



int[] evenNumbers(int[] numbers)

{

    import std.array : array;

    import std.algorithm : filter;



    return numbers.filter!(n => n % 2 == 0).array;

}



void main()

{

    writeln([1, 2, 3, 4].evenNumbers);

}

Compile it with your favorite D compiler and try it out. As expected, it produces the same output:

$ dmd ufcs_demo.d

$ ./ufcs_demo

[2, 4]

During compilation, the compiler automatically places the array as the first argument to the function. This is a regular pattern that makes using D such a joy, so it very much feels the same as you naturally think about your code. The result is functional-style programming.

You can probably guess what this prints:

//file: cool.d

import std.stdio : writeln;

import std.uni : asLowerCase, asCapitalized;



void main()

{

    string mySentence = "D IS COOL";

    writeln(mySentence.asLowerCase.asCapitalized);

}

But just to confirm:

$ dmd cool.d

$ ./cool

D is cool

Combined with other D features, UFCS gives you the power to compose reusable code that has a natural flow to it without sacrificing convenience.

Time to try D

As I've written before, D is a great language for development. It's easy to install from the D download page, so download the compiler, take a look at the examples, and experience D for yourself.