Add comments marking workarounds for #2

Sources/Pool.swift

@@ -64,6 +64,7 @@ public final class Pool<Resource: AnyObject> {
     }
 }
 
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 private protocol _ByIdentityProtocol: Hashable {
     associatedtype Object: AnyObject
     init(_ object: Object)
@@ -76,6 +77,7 @@ private struct ByIdentity<Object: AnyObject> {
     }
 }
 
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 extension ByIdentity: Hashable, _ByIdentityProtocol {
     static func == (lhs: ByIdentity, rhs: ByIdentity) -> Bool {
         return ObjectIdentifier(lhs.object) == ObjectIdentifier(rhs.object)
@@ -86,6 +88,7 @@ extension ByIdentity: Hashable, _ByIdentityProtocol {
     }
 }
 
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 extension Dictionary where Key: _ByIdentityProtocol {
     subscript(key: Key.Object) -> Value? {
         get {

Sources/SQLConnection.swift

@@ -8,11 +8,14 @@
 
 import Foundation
 
+/// Implementation detail used to detect SQLConnections in generics. Do not use.
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 public protocol _SQLConnection {
     associatedtype Client: SQLClient
 }
 
 // WORKAROUND: #1 Swift doesn't support `where` clauses on associated types
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 public final class SQLConnection<C: SQLClient>: _SQLConnection where C.RowStateSequence.Iterator.Element == C.RowState {
     public typealias Client = C
     public var state: Client.ConnectionState

Sources/SQLDatabase.swift

@@ -47,6 +47,7 @@ public struct SQLDatabase<Client: SQLClient> where Client.RowStateSequence.Itera
     }
 }
 
+// WORKAROUND: #2 Swift doesn't support same-type requirements on generics
 extension Pool where Resource: _SQLConnection, Resource.Client.RowStateSequence.Iterator.Element == Resource.Client.RowState {
     /// Creates a pool of connections to the given database.
     ///