Explainer on function visibility in runtime pallets

[gnunicorn]

Explain the difference between fn in the define block and fn and pub fn in an extra impl-Block in a substrate pallet. Do they differ? How? Which one to use when?

[JoshOrndorff]

You mean the difference between

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		// These function
	}
}

and

impl<T: Trait> Module<T> {
	// These functions
}

[gnunicorn]

yeah and more precisely on:

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		pub fn a() { }

		fn b(){ }
	}
}

impl<T: Trait> Module<T> {
	pub fn c() { }
	fn d() { }
}

the visibility of a, b, c and d to different parties.