Zero Cost Abstractions

Structures defined like this are called Zero Sized Types, as they contain no actual data. Although these types act “real” at compile time - you can copy them, move them, take references to them, etc., however the optimizer will completely strip them away.

The GpioConfig we return never exists at runtime. Calling this function will generally boil down to a single assembly instruction - storing a constant register value to a register location. This means that the type state interface we’ve developed is a zero cost abstraction - it uses no more CPU, RAM, or code space tracking the state of , and renders to the same machine code as a direct register access.

For complex or deeply nested structures, it may be tedious to define all possible combinations of state. In these cases, macros may be used to generate all implementations.