Szathmáry László honlapja @ DEIK

Select an element randomly.

(1) templates

import std.stdio;

T my_choice(T)(const T[] collection)
{
import std.random : uniform;

auto idx = uniform(0, collection.length); // [n, m) interval
return collection[idx];
}

void main()
{
int[] numbers = [8, 5, 1, 3];

writeln(my_choice(numbers)); // 3
writeln(my_choice(numbers)); // 5

// ----------

string[] words = ["aa", "bb", "cc", "dd"];

writeln(my_choice(words)); // dd
writeln(my_choice(words)); // cc
}

D has a choice() function, see here. This is just an example how it could be implemented manually.

Adding type constraints

Let's say we want to call my_choice() with string slices and int slices only. If the function is called with a different type, it should be a compile error.

(2) type constraints

import std.stdio;
import std.traits; // from here

// here: vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
T my_choice(T)(const T[] collection) if (is(T == int) || is(T == string))
{
import std.random : uniform;

auto idx = uniform(0, collection.length); // [n, m) interval
return collection[idx];
}

void main()
{
int[] numbers = [8, 5, 1, 3];
writeln(my_choice(numbers)); // OK

// ----------

string[] words = ["aa", "bb", "cc", "dd"];
writeln(my_choice(words)); // OK

// ----------

double[] scores = [3.1, 2.6, 8.7];
writeln(my_choice(scores)); // Error
}

Templates

Adding type constraints