Function va_arg 

pub unsafe fn va_arg<T: VaArgSafe>(ap: &mut VaListImpl<'_>) -> T

🔬This is a nightly-only experimental API. (core_intrinsics)

Loads an argument of type T from the va_list ap and increment the argument ap points to.

Safety

This function is only sound to call when:

• there is a next variable argument available.
• the next argument’s type must be ABI-compatible with the type T.
• the next argument must have a properly initialized value of type T.

Calling this function with an incompatible type, an invalid value, or when there are no more variable arguments, is unsound.