custom weight function wrapper

paint/example/src/lib.rs

@@ -482,6 +482,15 @@ decl_module! {
 			Ok(())
 		}
 
+		// TODO: this stuff will move to a new test.
+		#[weight = sr_primitives::weights::FunctionOf(
+			|args: (&u32, &T::AccountId, &BalanceOf<T>)| (args.0 + 100) as Weight,
+			1u8,
+		)]
+		fn blah(origin, _a: u32, _b: T::AccountId, _c: BalanceOf<T>) {
+			let _ = ensure_signed(origin);
+		}
+
 		/// A privileged call; in this case it resets our dummy value to something new.
 		// Implementation of a privileged call. The `origin` parameter is ROOT because
 		// it's not (directly) from an extrinsic, but rather the system as a whole has decided
@@ -774,5 +783,10 @@ mod tests {
 		let custom_call = <Call<Test>>::set_dummy(20);
 		let info = custom_call.get_dispatch_info();
 		assert_eq!(info.weight, 2000);
+
+		// must have arg.0 + 100
+		let custom_call = <Call<Test>>::blah(20u32, 1, 1);
+		let info = custom_call.get_dispatch_info();
+		assert_eq!(info.weight, 120);
 	}
 }

primitives/sr-primitives/src/weights.rs

@@ -110,6 +110,16 @@ impl Default for DispatchClass {
 	}
 }
 
+impl From<u8> for DispatchClass {
+	fn from(x: u8) -> Self {
+		match x {
+			0 => DispatchClass::Normal,
+			1 => DispatchClass::Operational,
+			_ => panic!("Reserved for other dispatch classes."),
+		}
+	}
+}
+
 impl From<SimpleDispatchInfo> for DispatchClass {
 	fn from(tx: SimpleDispatchInfo) -> Self {
 		match tx {
@@ -219,3 +229,25 @@ impl SimpleDispatchInfo {
 		Self::FixedNormal(0)
 	}
 }
+
+pub struct FunctionOf<F, Class>(pub F, pub Class);
+
+impl<Args, F, Class> WeighData<Args> for FunctionOf<F, Class>
+where
+	F : Fn(Args) -> Weight
+{
+	fn weigh_data(&self, args: Args) -> Weight {
+		(self.0)(args)
+	}
+}
+
+impl<Args, F, Class> ClassifyDispatch<Args> for FunctionOf<F, Class>
+where
+	Class: Into<DispatchClass> + Clone,
+{
+	fn classify_dispatch(&self, _: Args) -> DispatchClass {
+		self.1.clone().into()
+	}
+}
+
+// TODO: test these stuff with a dedicated `decl_module`. Needs relocating to support first. #4124