# urllibparse

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TL;DR: I’ve translated Python’s urllib.parse to D for parsing, building and transforming URLs. You can get it from Gitlab.

URL handling is one of those things that most of the time can be done with a regex that mostly works. But sometimes I want a just-works tool when writing D, so I translated Python’s URL handling library. The API isn’t perfect (e.g., the url_split and url_parse distinction is a bit confusing), but it’s been tested against multiple RFCs and had plenty of real-world battle hardening.

My translation is meant to give the same output as Python does, so I’ve translated the Python test suite as well. I don’t plan to add any new features that aren’t in Python.

I hope someone else finds it useful.

# Analysing D Code with KLEE

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KLEE is a symbolic execution engine that can rigorously verify or find bugs in software. It’s designed for C and C++, but it’s just an interpreter for LLVM bitcode combined with theorem prover backends, so it can work with bitcode generated by ldc2. One catch is that it needs a compatible bitcode port of the D runtime to run normal D code. I’m still interested in getting KLEE to work with normal D code, but for now I’ve done some experiments with -betterC D.

# Profiling D's Garbage Collection with Bpftrace

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Recently I’ve been playing around with using bpftrace to trace and profile D’s garbage collector. Here are some examples of the cool stuff that’s possible.

# D as a C Replacement

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Sircmpwn (the main developer behind the Sway Wayland compositor) recently wrote a blog post about how he thinks Rust is not a good C replacement. I don’t know if he’d like the D programming language either, but it’s become a C replacement for me.

# D in the Browser with Emscripten, LDC and bindbc-sdl (translation)

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Here’s a tutorial about using Emscripten to run D code in a normal web browser. It’s uses a different approach from the Dscripten game demo and the dscripten-tools toolchain that’s based on it.

• Instead of porting the D runtime, it uses a lightweight, runtimeless -betterC build.
• It uses Docker to manage the Emscripten installation.

LDC has recently gained support for compiling directly to WebAssembly, but (unlike the Emscripten approach) that doesn’t automatically get you libraries.

You can find the complete working code on Github. ./run.sh starts a shell in a Docker image that contains the development environment. dub build --build=release generates the HTML and JavaScript assets and puts them into the dist/ directory.

This tutorial is translated from a Japanese post by outlandkarasu, who deserves all the credit for figuring this stuff out.

# Understanding a *nix Shell by Writing One

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A typical *nix shell has a lot of programming-like features, but works quite differently from languages like Python or C++. This can make a lot of shell features — like process management, argument quoting and the export keyword — seem like mysterious voodoo.

But a shell is just a program, so a good way to learn how a shell works is to write one. I’ve written a simple shell that fits in a few hundred lines of commented D source. Here’s a post that walks through how it works and how you could write one yourself.

# Using D Features to Reimplement Inheritance and Polymorphism

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Some months ago I showed how inheritance and polymorphism work in compiled languages by reimplementing them with basic structs and function pointers. I wrote that code in D, but it could be translated directly to plain old C. In this post I’ll show how to take advantage of D’s features to make DIY inheritance a bit more ergonomic to use.

Although I have used these tricks in real code, I’m honestly just writing this because I think it’s neat what D can do, and because it helps explain how high-level features of D can be implemented — using the language itself.

# Hacking extern(C++) Classes to Work in betterC

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First up, here’s a big disclaimer if the title didn’t warn you enough: this is a hack. It’s just a proof-of-concept for getting extern(C++) classes working with betterC D. Also, DMD keeps getting better quickly, so if you’re reading this post when something more recent than version 2.080 is out, this hack is probably obsolete. Hopefully you’ll find this post interesting anyway if you’re either

• Interested in all things -betterC, or
• Curious about how stuff like classes work in D.

If you haven’t read my earlier post about how polymorphism and inheritance work yet, I recommend doing that first.

# Xanthe Doesn't Need Linker Hacking Now

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I finally got around to dusting off the code for Xanthe to test if it can work without linker hacking, now, too. Short answer: yes. I had to add an implementation of memcmp for the freestanding build, but other than that, all I had to do was throw away the linker hacking steps in the Makefile. Apart from the linker scripts for building the disk images, Xanthe now just compiles normally with -betterC.

Also, the old build was about twice as big as it needed to be because the media files were being packed into the binary twice for no good reason. That doesn’t seem to be a problem any more with the latest dmd.

# How Inheritance and Polymorphism Work

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I’ve promised to write a blog post about the DIY polymorphic classes implementation in Xanthe, the experimental game I once wrote for bare-metal X86. But first, I decided to write a precursor post that explains how polymorphism and inheritance work in the first place.