From 59ba8206e2fce4c68b0e37d560883e34c3904d49 Mon Sep 17 00:00:00 2001
From: Gav Wood <gavin@parity.io>
Date: Tue, 27 Apr 2021 12:00:20 +0200
Subject: [PATCH 1/2] Introduce macro for building Contains impl based on a
 match

---
 frame/support/src/traits/members.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/frame/support/src/traits/members.rs b/frame/support/src/traits/members.rs
index 35748ca9c0c07..86b7e1f9fcda0 100644
--- a/frame/support/src/traits/members.rs
+++ b/frame/support/src/traits/members.rs
@@ -31,6 +31,18 @@ impl<T: Ord> Contains<T> for All<T> {
 	fn contains(_: &T) -> bool { true }
 }
 
+#[macro_export]
+macro_rules! match_type {
+	( pub type $n:ident: impl Contains<$t:ty> = { $phead:pat $( | $ptail:pat )* } ; ) => {
+		pub struct $n;
+		impl $crate::traits::Contains<$t> for $n {
+			fn contains(l: &$t) -> bool {
+				matches!(l, $phead $( | $ptail )* )
+			}
+		}
+	}
+}
+
 /// A trait for a set which can enumerate its members in order.
 pub trait SortedMembers<T: Ord> {
 	/// Get a vector of all members in the set, ordered.

From ce7bcd5baaca83bc34b9b03b402318ee82347b53 Mon Sep 17 00:00:00 2001
From: Gav Wood <gavin@parity.io>
Date: Tue, 27 Apr 2021 13:30:45 +0200
Subject: [PATCH 2/2] Fixes

---
 frame/support/src/traits/members.rs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/frame/support/src/traits/members.rs b/frame/support/src/traits/members.rs
index 86b7e1f9fcda0..125f096fa92e1 100644
--- a/frame/support/src/traits/members.rs
+++ b/frame/support/src/traits/members.rs
@@ -31,6 +31,8 @@ impl<T: Ord> Contains<T> for All<T> {
 	fn contains(_: &T) -> bool { true }
 }
 
+/// Create a type which implements the `Contains` trait for a particular type with syntax similar
+/// to `matches!`.
 #[macro_export]
 macro_rules! match_type {
 	( pub type $n:ident: impl Contains<$t:ty> = { $phead:pat $( | $ptail:pat )* } ; ) => {
@@ -43,6 +45,22 @@ macro_rules! match_type {
 	}
 }
 
+#[cfg(test)]
+mod tests {
+	use super::*;
+
+	match_type! {
+		pub type OneOrTenToTwenty: impl Contains<u8> = { 1 | 10..=20 };
+	}
+
+	#[test]
+	fn match_type_works() {
+		for i in 0..=255 {
+			assert_eq!(OneOrTenToTwenty::contains(&i), i == 1 || i >= 10 && i <= 20);
+		}
+	}
+}
+
 /// A trait for a set which can enumerate its members in order.
 pub trait SortedMembers<T: Ord> {
 	/// Get a vector of all members in the set, ordered.