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Learn D - 10 Code Examples & CST Typing Practice Test

D is a high-level, statically typed, compiled systems programming language combining C-like performance with modern features like garbage collection, functional programming, and meta-programming.

View all 10 D code examples →
D Counter and Theme ToggleD Simple AdditionD FactorialD Fibonacci SequenceD Max of Two NumbersD Array SumD Even Numbers FilterD Conditional Counter IncrementD Resettable CounterD Theme Toggle Only

Learn D with Real Code Examples

Updated Nov 20, 2025

Explain

D supports imperative, object-oriented, and functional programming paradigms.

It offers safe systems-level programming with modern abstractions.

Templates, mixins, and compile-time reflection enable advanced metaprogramming.

Core Features

Strong static typing with type inference

Modules and package system

Function overloading, operator overloading

First-class functions and closures

Compile-time reflection and code generation

Basic Concepts Overview

Variables, constants, and types

Functions and procedures

Control flow: if, while, for, switch

Structs, classes, and interfaces

Modules, packages, and imports

Project Structure

src/ - D source files

tests/ - unit and integration tests

dub.json - project configuration and dependencies

examples/ - sample programs

docs/ - project documentation

Building Workflow

Write source code (.d files)

Compile using dmd, ldc, or gdc

Use Dub for dependencies and builds

Run unit tests with built-in test blocks

Deploy native binaries across platforms

Difficulty Use Cases

Beginner: basic scripts, control flow, functions

Intermediate: classes, templates, operator overloading

Advanced: compile-time reflection, mixins, ranges

Expert: game engines, high-performance computing, concurrency

Research: DSLs, metaprogramming, compiler extensions

Comparisons

Similar performance to C++

Higher-level features than C/C++

Easier syntax than C++ templates

Smaller ecosystem than Rust or Go

Better compile-time metaprogramming than most mainstream languages

Versioning Timeline

1999 - D initial design by Walter Bright

2001 - D1 language released

2007 - D2 language released with modern features

2010s - Growth of ecosystem and community

2020s - Active development and library expansion

Glossary

Struct: value-type user-defined type

Class: reference-type user-defined type

Template: generic code construct

Mixin: compile-time code insertion

Range: iterable sequence abstraction

Installation Setup

Install DMD (D Compiler), LDC, or GDC

Verify installation with dmd --version

Set PATH for compiler binaries

Install Dub package manager

Test setup with simple hello world program

Environment Setup

Install DMD, LDC, or GDC compiler

Set PATH for D binaries

Install Dub package manager

Optional: configure IDE (VS Code, Vim, Emacs)

Test compiler with simple hello world

Config Files

dub.json or dub.sdl for project config

.d source files

Build scripts for deployment

Test scripts for automated validation

Documentation and examples

Cli Commands

dmd file.d # compile

dub build # build project with Dub

dub test # run unit tests

ldc2 file.d # alternative compiler

gdc file.d # GCC-based D compiler

Internationalization

Supports Unicode and UTF-8

Used globally for systems and web programming

Libraries handle locale-specific tasks

Documentation available in multiple languages

Web frameworks allow multi-language UI support

Accessibility

Cross-platform support (Windows, Linux, macOS)

Active documentation and community

Lightweight compiler and tooling

Dub for easy package management

GitHub and forums for support

Ui Styling

No built-in GUI

Console I/O via std.stdio

Web UI via Vibe.d or other frameworks

External libraries for GUI integration

CLI-focused development

State Management

Garbage-collected by default

Structs and classes encapsulate state

Modules manage global state

Contracts verify state correctness

Templates and mixins can manipulate state at compile-time

Data Management

Primitive types: int, float, bool, char

Structs and classes for structured data

Arrays, dynamic arrays, associative arrays

Ranges for iterable sequences

Compile-time data manipulation via templates/mixins

Architecture

Compiled to native code

Supports both garbage-collected and manual memory management

Modules and packages organize code

Templates and mixins allow code reuse and metaprogramming

Contracts and unit tests improve reliability

Rendering Model

Source code compiled to native binaries

Modules organize code into packages

Templates and mixins generate code at compile-time

Contracts and unittest blocks enforce correctness

Binaries executed across platforms natively

Architectural Patterns

Procedural and functional pipelines

OOP for encapsulation

Compile-time code generation using templates/mixins

Range-based iteration

Module/package-based project organization

Real World Architectures

Game engines and physics simulations

High-performance computing

Web backends with Vibe.d

Financial and trading applications

System utilities and CLI tools

Design Principles

C-like syntax with modern safety features

Multi-paradigm: imperative, OOP, functional

Compile-time metaprogramming with templates and mixins

Garbage collection for managed memory

Focus on performance and expressiveness

Scalability Guide

Use modules/packages for large projects

Leverage templates and mixins for reusable code

Profile performance-critical sections

Optimize memory usage

Parallelize tasks where possible

Migration Guide

Port older D1 code to D2

Refactor templates for modern syntax

Update deprecated standard library usage

Test performance after migration

Ensure cross-platform compatibility

Performance Notes

Compile to native with optimizations

Use manual memory management for real-time performance

Leverage ranges to reduce memory allocations

Profile with D's built-in tools

Avoid unnecessary garbage collection triggers

Security Notes

Use contracts to enforce invariants

Validate inputs for security-critical applications

Avoid unsafe casts or pointer manipulation

Handle exceptions appropriately

Use static typing to prevent type-related bugs

Monitoring Analytics

Profile execution speed

Analyze memory usage

Debug template and mixin code

Check range iteration performance

Log critical operations in production

Code Quality

Use contracts and unit tests

Follow strong typing and conventions

Modularize projects with packages

Leverage templates/mixins carefully

Document classes, structs, and procedures

Practical Examples

Hello world CLI

Range-based iteration example

Template function for generic containers

Class with inheritance and interfaces

Compile-time mixin code generation

Troubleshooting

Resolve type mismatches

Check template constraints

Ensure correct module imports

Fix memory management issues

Verify compile-time mixin syntax

Testing Guide

Use built-in unittest blocks

Check contracts for invariants

Test template-generated code

Validate concurrency and async code

Profile performance and memory usage

Deployment Options

Native binaries for Linux, Windows, macOS

Dockerized deployment for web backends

Game engine executables

Financial and scientific applications

Cross-platform CLI tools

Tools Ecosystem

DMD, LDC, GDC compilers

Dub package manager

Vibe.d for web backends

Derelict for C interop

Phobos standard library

Integrations

Interop with C and C++

Web frameworks like Vibe.d

Scientific libraries for numerical computing

Game engine development

Compile-time metaprogramming and DSLs

Productivity Tips

Use Dub for project and dependency management

Write unittest blocks early

Profile and optimize code iteratively

Use templates/mixins for repetitive patterns

Organize code with modules/packages

Challenges

Build CLI calculator

Implement generic container using templates

Create a web server with Vibe.d

Develop high-performance numeric application

Use compile-time mixins for repetitive code

Learning Path

Learn basic syntax and control flow

Understand structs, classes, and interfaces

Explore templates and ranges

Practice compile-time reflection and mixins

Build real-world applications with Dub

Skill Improvement Plan

Week 1: Syntax, variables, functions

Week 2: Classes, structs, inheritance

Week 3: Templates, ranges, mixins

Week 4: Performance tuning and concurrency

Interview Questions

What are D templates?

How does D support compile-time code execution?

Explain garbage collection in D

Difference between struct and class?

What are ranges and how are they used?

Cheat Sheet

import std.stdio;

int x = 10;

void main() { writeln("Hello World"); }

struct S { int a; }

template mixinExample() { ... }

Books

The D Programming Language by Andrei Alexandrescu

Learning D

Programming in D

Mastering D

Practical D Applications

Tutorials

Getting started with D

D templates and mixins

Concurrency and ranges in D

Building web applications with Vibe.d

Advanced D programming patterns

Official Docs

D Language Official Documentation

D Language Reference

Dub Package Manager Documentation

Community Links

D forum

StackOverflow D tag

Reddit r/d_language

GitHub D repositories

Discord D community

Community Support

D language forum

StackOverflow D tag

Reddit r/d_language

GitHub D repositories

Discord D community

Monetization

Game engine development

High-performance computing tools

Financial software

Web backend services

System utilities and CLI tools

Future Roadmap

Enhanced library ecosystem

Better concurrency and parallelism support

Improved IDE tooling

Expanded web framework support

Growing adoption in performance-critical domains

When Not To Use

Large-scale GUI-heavy desktop applications

Projects needing massive library ecosystems

Embedded systems with strict real-time constraints

Rapid prototyping with minimal setup

Applications requiring maximum portability with minimal compilation

Final Summary

D is a versatile systems programming language with high-performance and modern abstractions.

Supports multi-paradigm development and compile-time metaprogramming.

Ideal for system tools, games, web backends, and scientific computing.

Faq

Is D still relevant?

Yes - used in high-performance and systems programming.

Is D compiled or interpreted?

Compiled to native binaries.

Is D functional or imperative?

Supports imperative, OOP, and functional paradigms.

Can D be used for web development?

Yes - via Vibe.d and other web libraries.

Code Sample Descriptions

1

D Counter and Theme Toggle

import std.stdio;

int count = 0;
bool isDark = false;

void updateUI() {
    writeln("Counter: ", count);
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

void increment() {
    count += 1;
    updateUI();
}

void decrement() {
    count -= 1;
    updateUI();
}

void reset() {
    count = 0;
    updateUI();
}

void toggleTheme() {
    isDark = !isDark;
    updateUI();
}

// Simulate actions
updateUI();
increment();
increment();
toggleTheme();
decrement();
reset();

Demonstrates a simple counter with theme toggling using D variables and console output.

Let’s Try →
2

D Simple Addition

import std.stdio;
void main() {
    int a = 10;
    int b = 20;
    int sum = a + b;
    writeln("Sum: ", sum);
}

Adds two numbers and prints the result.

Let’s Try →
3

D Factorial

import std.stdio;
int factorial(int n) {
    return n <= 1 ? 1 : n * factorial(n - 1);
}
void main() {
    writeln("Factorial 5: ", factorial(5));
}

Calculates factorial recursively.

Let’s Try →
4

D Fibonacci Sequence

import std.stdio;
int fib(int n) {
    return n < 2 ? n : fib(n - 1) + fib(n - 2);
}
void main() {
    foreach(i; 0 .. 10)
        writeln(fib(i));
}

Generates first 10 Fibonacci numbers.

Let’s Try →
5

D Max of Two Numbers

import std.stdio;
void main() {
    int a = 10, b = 20;
    int max = a > b ? a : b;
    writeln("Max: ", max);
}

Finds the maximum of two numbers.

Let’s Try →
6

D Array Sum

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    int sum = 0;
    foreach(x; arr)
        sum += x;
    writeln("Sum: ", sum);
}

Sums elements of an array.

Let’s Try →
7

D Even Numbers Filter

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    foreach(x; arr)
        if(x % 2 == 0)
        writeln(x);
}

Prints even numbers from an array.

Let’s Try →
8

D Conditional Counter Increment

import std.stdio;
void main() {
    int count = 3;
    if(count < 5)
        count++;
    writeln("Count: ", count);
}

Increment counter only if less than 5.

Let’s Try →
9

D Resettable Counter

import std.stdio;
void main() {
    int count = 0;
    count += 1;
    count += 1;
    writeln("Count: ", count);
    count = 0;
    writeln("Count: ", count);
}

Counter that increments and can be reset.

Let’s Try →
10

D Theme Toggle Only

import std.stdio;
void main() {
    bool isDark = false;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

Toggles theme multiple times.

Let’s Try →

Frequently Asked Questions about D

What is D?

D is a high-level, statically typed, compiled systems programming language combining C-like performance with modern features like garbage collection, functional programming, and meta-programming.

What are the primary use cases for D?

Systems programming and OS-level development. High-performance computing. Game engines and graphics programming. Financial and trading applications. Compile-time code generation and metaprogramming

What are the strengths of D?

High-performance native code. Clean modern syntax with C-style familiarity. Powerful compile-time metaprogramming. Versatile multi-paradigm language. Rich standard library with ranges and algorithms

What are the limitations of D?

Smaller community and ecosystem than C++ or Rust. Less industrial adoption for large-scale projects. Limited GUI library support. Garbage collector can be unpredictable in real-time systems. Interfacing with C++ can be complex

How can I practice D typing speed?

CodeSpeedTest offers 10+ real D code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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