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Advanced Programming Techniques in D

Function Pointer as a Parameter & a Member

Explore how to define and use function pointers as parameters and members in D programming. Understand how to parameterize filtering and conversion behaviors, create reusable algorithms, and employ concise anonymous functions for clearer code.

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Function pointer as a parameter

Let’s design a function that takes an array and returns another array. This function will filter out elements with values less than or equal to zero and multiply the others by ten:

D
int[] filterAndConvert(const int[] numbers) {

    int[] result;

    

    foreach (e; numbers) {

        if (e > 0) { // filtering,

            immutable newNumber = e * 10; // and conversion

            result ~= newNumber; 

        }

    }

    

    return result;

}

The following program demonstrates its behavior with randomly generated values:

D
import std.stdio; 

import std.random;



int[] filterAndConvert(const int[] numbers) {

    int[] result;

    

    foreach (e; numbers) {

        if (e > 0) { // filtering,

            immutable newNumber = e * 10; // and conversion

            result ~= newNumber; 

        }

    }

    

    return result;

}



void main() {

    int[] numbers;

    // Random numbers

    foreach (i; 0 .. 10) {

        numbers ~= uniform(0, 10) - 5;

    }

    

    writeln("input : ", numbers);

    writeln("output: ", filterAndConvert(numbers)); 

}

The output contains numbers that ...