Introduce FailableIterator

Sources/SQLite/Core/Statement.swift

@@ -191,14 +191,6 @@ public final class Statement {
 
 }
 
-extension Statement {
-
-    func rowCursorNext() throws -> [Binding?]? {
-        return try step() ? Array(row) : nil
-    }
-
-}
-
 extension Statement : Sequence {
 
     public func makeIterator() -> Statement {
@@ -208,12 +200,38 @@ extension Statement : Sequence {
 
 }
 
-extension Statement : IteratorProtocol {
+public protocol FailableIterator : IteratorProtocol {
+    func failableNext() throws -> Self.Element?
+}
 
-    public func next() -> [Binding?]? {
-        return try! step() ? Array(row) : nil
+extension FailableIterator {
+    public func next() -> Element? {
+        return try! failableNext()
     }
 
+    public func map<T>(_ transform: (Element) throws -> T) throws -> [T] {
+        var elements = [T]()
+        while let row = try failableNext() {
+            elements.append(try transform(row))
+        }
+        return elements
+    }
+}
+
+extension Array {
+    public init<I: FailableIterator>(_ failableIterator: I) throws where I.Element == Element {
+        self.init()
+        while let row = try failableIterator.failableNext() {
+            append(row)
+        }
+    }
+}
+
+extension Statement : FailableIterator {
+    public typealias Element = [Binding?]
+    public func failableNext() throws -> [Binding?]? {
+        return try step() ? Array(row) : nil
+    }
 }
 
 extension Statement : CustomStringConvertible {

Sources/SQLite/Typed/Query.swift

@@ -894,35 +894,19 @@ public struct Delete : ExpressionType {
 
 }
 
-public struct RowCursor {
+
+public struct RowCursor: FailableIterator {
+    public typealias Element = Row
     let statement: Statement
     let columnNames: [String: Int]
-
-    public func next() throws -> Row? {
-        return try statement.rowCursorNext().flatMap { Row(columnNames, $0) }
-    }
-
-    public func map<T>(_ transform: (Row) throws -> T) throws -> [T] {
-        var elements = [T]()
-        while true {
-            if let row = try next() {
-                elements.append(try transform(row))
-            } else {
-                break
-            }
-        }
-
-        return elements
+
+    public func failableNext() throws -> Row? {
+        return try statement.failableNext().flatMap { Row(columnNames, $0) }
     }
 }
 
+
 extension Connection {
-
-    public func prepareCursor(_ query: QueryType) throws -> RowCursor {
-        let expression = query.expression
-        let statement = try prepare(expression.template, expression.bindings)
-        return RowCursor(statement: statement, columnNames: try columnNamesForQuery(query))
-    }
 
     public func prepare(_ query: QueryType) throws -> AnySequence<Row> {
         let expression = query.expression
@@ -935,6 +919,12 @@ extension Connection {
         }
     }
 
+    public func prepareRowCursor(_ query: QueryType) throws -> RowCursor {
+        let expression = query.expression
+        let statement = try prepare(expression.template, expression.bindings)
+        return RowCursor(statement: statement, columnNames: try columnNamesForQuery(query))
+    }
+
     private func columnNamesForQuery(_ query: QueryType) throws -> [String: Int] {
         var (columnNames, idx) = ([String: Int](), 0)
         column: for each in query.clauses.select.columns {
@@ -1002,7 +992,7 @@ extension Connection {
     }
 
     public func pluck(_ query: QueryType) throws -> Row? {
-        return try prepareCursor(query.limit(1, query.clauses.limit?.offset)).next()
+        return try prepareRowCursor(query.limit(1, query.clauses.limit?.offset)).failableNext()
     }
 
     /// Runs an `Insert` query.

Tests/SQLiteTests/QueryTests.swift

@@ -343,14 +343,14 @@ class QueryIntegrationTests : SQLiteTestCase {
             _ = user[users[managerId]]
         }
     }
-    
-    func test_prepareCursor() {
+
+    func test_prepareRowCursor() {
         let names = ["a", "b", "c"]
         try! InsertUsers(names)
-        
+
         let emailColumn = Expression<String>("email")
-        let emails = try! db.prepareCursor(users).map { $0[emailColumn] }
-        
+        let emails = try! db.prepareRowCursor(users).map { $0[emailColumn] }
+
         XCTAssertEqual(names.map({ "\($0)@example.com" }), emails.sorted())
     }