[pdsl_model] Extend messages! macro with manual identifiers

model/examples/adder.rs

@@ -18,9 +18,9 @@ state! {
 
 messages! {
 	/// Increases the storage value by the given amount.
-	Inc(by: u32);
+	0 => Inc(by: u32);
 	/// Returns the storage value.
-	Get() -> u32;
+	1 => Get() -> u32;
 }
 
 fn instantiate() -> impl Contract {

model/examples/erc20.rs

@@ -26,13 +26,13 @@ state! {
 
 messages! {
 	/// Returns the total supply.
-	TotalSupply() -> Balance;
+	0 => TotalSupply() -> Balance;
 	/// Returns the balance of the given address.
-	BalanceOf(owner: Address) -> Balance;
+	1 => BalanceOf(owner: Address) -> Balance;
 	/// Transfers balance from the caller to the given address.
 	///
 	/// Returns `true` if the transfer was successful.
-	Transfer(to: Address, amount: Balance) -> bool;
+	2 => Transfer(to: Address, amount: Balance) -> bool;
 }
 
 fn instantiate() -> impl Contract {

model/src/lib.rs

 #![cfg_attr(not(feature = "std"), no_std)]
-
 #![feature(
 	const_fn,
 	const_str_as_bytes,
 )]
-
 #![allow(unused)]
 
 #[macro_use]

model/src/msg.rs

+use crate::{
+	msg_handler::MessageHandlerSelector,
+};
 
 /// A message with an expected input type and output (result) type.
 pub trait Message {
@@ -7,6 +10,11 @@ pub trait Message {
 	/// The output of the message, also known as return type.
 	type Output: parity_codec::Encode;
 
+	/// The user provided message selector.
+	///
+	/// This identifier must be unique for every message.
+	const ID: MessageHandlerSelector;
+
 	/// The name of the message.
 	///
 	/// # Note
@@ -19,7 +27,8 @@ pub trait Message {
 #[macro_export]
 macro_rules! messages {
 	(
-		$( #[$msg_meta:meta] )* $msg_name:ident (
+		$( #[$msg_meta:meta] )*
+		$msg_id:literal => $msg_name:ident (
 			$( $param_name:ident : $param_ty:ty ),*
 		) -> $ret_ty:ty ;
 
@@ -33,19 +42,28 @@ macro_rules! messages {
 			type Input = ($($param_ty),*);
 			type Output = $ret_ty;
 
+			const ID: $crate::MessageHandlerSelector = $crate::MessageHandlerSelector::new($msg_id);
 			const NAME: &'static [u8] = stringify!($msg_name).as_bytes();
 		}
 
 		messages!($($rest)*);
 	};
 	(
-		$( #[$msg_meta:meta] )* $msg_name:ident (
+		$( #[$msg_meta:meta] )*
+		$msg_id:literal => $msg_name:ident (
 			$( $param_name:ident : $param_ty:ty ),*
 		) ;
 
 		$($rest:tt)*
 	) => {
-		messages!( $( #[$msg_meta] )* $msg_name ( $( $param_name : $param_ty ),* ) -> (); $($rest)* );
+		messages!(
+			$( #[$msg_meta] )*
+			$msg_id => $msg_name (
+				$( $param_name : $param_ty ),*
+			) -> ();
+
+			$($rest)*
+		);
 	};
 	() => {};
 }

model/src/msg_handler.rs

@@ -70,7 +70,14 @@ impl CallData {
 
 /// A hash to identify a called function.
 #[derive(Copy, Clone, PartialEq, Eq)]
-pub struct MessageHandlerSelector(pub u64);
+pub struct MessageHandlerSelector(u32);
+
+impl MessageHandlerSelector {
+	/// Creates a new message handler selector from the given value.
+	pub const fn new(raw: u32) -> Self {
+		Self(raw)
+	}
+}
 
 /// A read-only message handler.
 ///

model/src/test.rs

@@ -18,9 +18,9 @@ state! {
 
 messages! {
 	/// Increases the storage value by the given amount.
-	Inc(by: u32);
+	0 => Inc(by: u32);
 	/// Returns the storage value.
-	Get() -> u32;
+	1 => Get() -> u32;
 }
 
 fn instantiate() {