Functions

Functions are declared the same as in C. In addition, D offers some convenience features like:

Uniform function call syntax (UFCS)

UFCS allows any call to a free function fun(a) to be written as a member function call: a.fun()

import std.algorithm : group;
import std.range : chain, dropOne, front, retro;

//retro(chain([1, 2], [3, 4]));
//front(dropOne(group([1, 1, 2, 2, 2])));

[1, 2].chain([3, 4]).retro; // 4, 3, 2, 1
[1, 1, 2, 2, 2].group.dropOne.front; // (2, 3)

Practice

Let’s go back to the practice/array-median directory. This time we want to find the median element using functions from the std.algorithm package. Use UFCS for an increase in expressiveness. Observe the increase in performance achieved by using functions from the standard library

Overloading:

import std.stdio : writefln;

void add(int a, int b)
{
    writefln("sum = %d", a + b);
}

void add(double a, double b)
{
    writefln("sum = %f", a + b);
}

void main()
{
    add(10, 2);
    add(5.3, 6.2);
}

Function overloading is a feature of object-oriented programming where two or more functions can have the same name but different parameters. Overloading is done based on the type of parameters, not on the return type.

Default parameters:

void fun(int a, int b=8) {}

void main()
{
    fun(7);    // calls fun(7, 8)
    fun(2, 3); // calls fun(2, 3)
}

A function may have any number of default parameters. If a default parameter is given, all following parameters must also have default values.

Auto return type:

auto fun()
{
    return 7;
}

void main()
{
    int b = fun();
    auto c = fun();   // works for variables also
}

Auto functions have their return type inferred based on the type of the return statements. Auto can be also used to infer the type of a variable declaration.

Practice

Navigate to the practice/voldemort directory. Result is a struct declared inside fun’s scope. However we want to be able to use it in main as well. Inspect the file. Does it compile? Why? Fix the issue.