Default Parameters

Do you want default function arguments or method parameters inside Rust?

Well, too bad! As this feature is currently not supported in Rust we can only emulate this functionality through macros and even more macros.

Formalisation

Default parameters could be easily formalised as

struct DefaultParam<T, const VAL: T>(T);

Reality

This approach however falls apart in a spectacular fashion as Rust doesn't support types dependent on other types.

Sadly this leaves us no choice. We can currently only make default arguments for integer, bool and char types.

How does this implementation work?

• All supported types have a wrapper around them (i32 -> Di32, bool -> Dbool ...)
• Empty default arguments can be created via

let def1=Di32::<23>::new(); // Its value will be 23

• Default arguments with values can be created via

let def2=Di32::<5>::from(53); // Its value will be 53

• The value of default arguments can be unwrapped via

assert_eq!(def1.unwrap(),23);
assert_eq!(def2.unwrap(),53);