Purify Contains, add IsInVec, All and SortedMembers (#8589)

* IsInVec

* Purify `Contains`, introduce SortedMembers

substrate/frame/support/src/traits/members.rs

@@ -17,16 +17,28 @@
 
 //! Traits for dealing with the idea of membership.
 
-use sp_std::prelude::*;
+use sp_std::{prelude::*, marker::PhantomData};
 
 /// A trait for querying whether a type can be said to "contain" a value.
-pub trait Contains<T: Ord> {
+pub trait Contains<T> {
 	/// Return `true` if this "contains" the given value `t`.
-	fn contains(t: &T) -> bool { Self::sorted_members().binary_search(t).is_ok() }
+	fn contains(t: &T) -> bool;
+}
 
+/// A `Contains` implementation which always returns `true`.
+pub struct All<T>(PhantomData<T>);
+impl<T: Ord> Contains<T> for All<T> {
+	fn contains(_: &T) -> bool { true }
+}
+
+/// 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.
 	fn sorted_members() -> Vec<T>;
 
+	/// Return `true` if this "contains" the given value `t`.
+	fn contains(t: &T) -> bool { Self::sorted_members().binary_search(t).is_ok() }
+
 	/// Get the number of items in the set.
 	fn count() -> usize { Self::sorted_members().len() }
 
@@ -38,6 +50,21 @@ pub trait Contains<T: Ord> {
 	fn add(_t: &T) { unimplemented!() }
 }
 
+/// Adapter struct for turning an `OrderedMembership` impl into a `Contains` impl.
+pub struct AsContains<OM>(PhantomData<(OM,)>);
+impl<T: Ord + Eq, OM: SortedMembers<T>> Contains<T> for AsContains<OM> {
+	fn contains(t: &T) -> bool { OM::contains(t) }
+}
+
+/// Trivial utility for implementing `Contains`/`OrderedMembership` with a `Vec`.
+pub struct IsInVec<T>(PhantomData<T>);
+impl<X: Eq, T: super::Get<Vec<X>>> Contains<X> for IsInVec<T> {
+	fn contains(t: &X) -> bool { T::get().contains(t) }
+}
+impl<X: Ord + PartialOrd, T: super::Get<Vec<X>>> SortedMembers<X> for IsInVec<T> {
+	fn sorted_members() -> Vec<X> { let mut r = T::get(); r.sort(); r }
+}
+
 /// A trait for querying bound for the length of an implementation of `Contains`
 pub trait ContainsLengthBound {
 	/// Minimum number of elements contained