PR #4 feedback: typed angles and value-move

What I’m trying to achieve

Walk through Saf’s review comments on PR #4, understand the underlying C++ idioms, and address each comment.

Research

One-copy-one-move idiom

Saf flagged withPos(Pos2 pos): the parameter is a copy, then this->pos = pos; is a second copy. For trivial types like the current Pos2 it is no different from a single copy at runtime, but the convention is to take by value and std::move into the member. That gives a single copy when the caller passes an lvalue, and zero copies when they pass a temporary.

Pass-by-value-and-move is an approach that handles both lvalue and rvalue arguments correctly, without surprising the caller.

Added std::move only on the Pos2 setter. Floats are trivial; adding std::move to the float setters would mislead readers into thinking there is something to steal.

Default constructors

Learned: the moment any constructor is written, the compiler stops generating the implicit default constructor for you. You have to explicitly opt back in with Foo() = default; if you want a default ctor. Vehicle, VehicleBuilder, and Entity get the implicit default for free, since they have no user-written ctors.

Angle and AngularVelocity types

Saf’s second comment: heading and steeringAngle were bare floats, and there is no signal at the call site whether they are radians or degrees. Solved with two new classes.

Angle stores its value canonically in radians (rad_). Construction goes through Angle::fromRadians(x) or Angle::fromDegrees(x). Accessors radians() and degrees() read out either way. operator+= lets heading += delta work.

AngularVelocity is the same shape, in radians per second. It has an operator*(float seconds) that returns an Angle, so angularVelocity * dt comes out cleanly typed.

The float-taking constructor is private and explicit. The private keyword blocks direct external construction; explicit blocks cheeky float-to-Angle conversions if we ever move the class to public and forget the whole point of the factories. In other words, the friction is the feature, and callers must name the unit at every construction site. This is the whole reason these types exist instead of using Angle = float;.

Style notes I learned worth logging

• Google convention: k-prefixed CamelCase for compile-time constants (kPi, kDegToRad, kRadToDeg), trailing-underscore for private data members (rad_).

Driving questions

• What pixel-to-metres scale makes the simulation feel right? Still open.
• What does steering input look like from a user’s perspective: keyboard, gamepad, mouse? What does it look like when it’s hard-coded?
• How sensitive is the kinematic update to tick rate / dt?
• Should Pos2 and Angle expose both + and += (and similar pairs), or only what the current call sites use?

Next

• Demo a simple car moving on screen with a basic rectangle sprite.
• Wire update() into the render loop with a real clock so dt is meaningful.