8 Design Patterns

8.1.4 Predictability

Constructors are used instead of extension traits (C-CTOR)

All peripherals to which the HAL adds functionality should be wrapped in a new type, even if no additional fields are required for that functionality.

Extension traits implemented for the raw peripheral should be avoided.

Methods are decorated with #[inline] where appropriate (C-INLINE)

The Rust compiler does not by default perform full inlining across crate boundaries. As embedded applications are sensitive to unexpected code size increases, #[inline] should be used to guide the compiler as follows:

• All “small” functions should be marked #[inline]. What qualifies as “small” is subjective, but generally all functions that are expected to compile down to single-digit instruction sequences qualify as small.
• Functions that are very likely to take constant values as parameters should be marked as #[inline]. This enables the compiler to compute even complicated initialization logic at compile time, provided the function inputs are known.