C++ without classes

content/programming/cxx-without-classes.tree

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+%% title = "C++ without Classes"
+
+- one thing I often see in people's code in C++ is putting _everything_ into a class.
+
+    - there's nothing wrong with putting code that actually, y'know, _uses the class_, in the class, but it irks me when I see things like helper functions and other implementation details being in the class.
+
+        - private functions have the unfortunate consequence of being part of the public header, even though they are implementation details!
+        this means if you edit them, you have to edit both the .cpp implementation file, as well as the .h header.
+
+- which is precisely what C++ without Classes is about.
+since updating method signatures is a pain in the ass... just don't do it!
+
+    - declare all your fields public, and let `static` functions within your `.cpp` file work the magic.
+
+        - and here you might say: "but I don't _want_ to have these fields public! it breaks encapsulation!"
+        to which I respond: so make your data structure private!
+
+- example of C++:
+
+#### world.h
+
+```cpp
+struct World
+{
+    // ... fields ...
+
+    void update(const Update_Context& context);
+
+private:
+    void update_aims(const Update_Context& context);
+};
+```
+
+#### world.cpp
+
+```cpp
+void World::update(const Update_Context& context)
+{
+    update_aims(context);
+}
+
+void World::update_aims(const Update_Context& context)
+{
+    // ...
+}
+```
+
+- example of C++ without Classes:
+
+#### world.h
+
+```cpp
+struct World
+{
+    // ... fields ...
+};
+
+void update(World& world, const Update_Context& context);
+```
+
+#### world.cpp
+
+```cpp
+static void update_aims(World& world, const Update_Context& context)
+{
+    // ...
+}
+
+void update(World& world, const Update_Context& context)
+{
+    update_aims(world, context);
+    // ...
+}
+```
+
+    - suddenly, the publicly available part of `world.h` has gotten smaller---there's one method less.
+    the implementation detail `update_aims` does not leak into the header; we don't have to update the signature in two places if we ever want to change it, and it does not cause a recompilation if we edit it.
+
+    - I took the `update` method out of the struct to signal the lack of coupling.
+    _anyone_ can do what `update` does; it doesn't matter.
+    every function is at the same level as the struct itself.
+
+    - in my own code, outside this contrived example, I also put functions related to a data structure in a namespace---in this case, `update(World&, const Update_Context&)` would be `world::update(World&, const Update_Context&)`.
+    this is purely a stylistic preference---I like the extra explicitness over leaning on overloads.
+
+- I've been enjoying this style a lot.
+it takes edge cases like `this` out of the language, and results in simpler, more easily editable code.
+so I wholeheartedly recommend giving it a try!