Thread safe lazy loading with double check lock optimization

Sources/WeaverDI/Builder.swift

@@ -7,62 +7,40 @@
 
 import Foundation
 
+/// A representation of any builder.
+protocol AnyBuilder {
+
+    var scope: Scope { get }
+}
+
 // MARK: - Builder
 
-final class Builder {
-
-    let scope: Scope
-    private let body: Any
+/// A `Builder` is an object responsible for lazily building the instance of a service.
+/// It is fully thread-safe.
+/// - Parameters
+///     - I: Instance type.
+///     - P: Parameters type. Usually a tuple containing multiple parameters (eg. `(p1: Int, p2: String, ...)`)
+final class Builder<I, P>: AnyBuilder {
 
-    private var instance: Instance?
-    private let locker = NSLock()
+    typealias Body = (() -> P) -> I
 
-    init(scope: Scope, body: Any) {
+    let scope: Scope
+
+    private var instance: Instance
+
+    /// Inits a builder.
+    /// - Parameters
+    ///     - scope: Service's scope used to determine which building & storing strategy to use.
+    ///     - body: Block responsible of calling the service's initializer (eg. `init(p1: Int, p2: String, ...)`).
+    init(scope: Scope, body: @escaping Body) {
         self.scope = scope
-        self.body = body
+        instance = Instance(scope: scope, body: body)
     }
 
-    func functor<P, I>() -> (() -> P) -> I {
-
-        guard let body = body as? (() -> P) -> I else {
-            fatalError("Type \(((() -> P) -> I).self) doesn't correspond to body type: \(self.body.self)")
-        }
-
-        guard !scope.isTransient else {
-            return body
-        }
-
+    /// Makes the builder's body, which can then get called to build the service's instance, and store it.
+    func make() -> Body {
         return { (parameters: () -> P) -> I in
-            self.locker.lock()
-            defer { self.locker.unlock() }
-
-            if let instance = self.instance?.value as? I {
-                return instance
-            }
-
-            let instance = body(parameters)
-            self.instance = Instance(value: instance as AnyObject, scope: self.scope)
-            return instance
+            return self.instance.getInstance(parameters: parameters)
         }
     }
 }
-
-// MARK: - Instance
-
-private final class Instance {
-    private weak var weakValue: AnyObject?
-    private var strongValue: AnyObject?
-
-    init(value: AnyObject, scope: Scope) {
-
-        if scope.isWeak {
-            weakValue = value
-        } else {
-            strongValue = value
-        }
-    }
-
-    var value: AnyObject? {
-        return weakValue ?? strongValue ?? nil
-    }
-}

Sources/WeaverDI/BuilderStore.swift

@@ -11,9 +11,9 @@ import Foundation
 
 protocol BuilderStoring: AnyObject {
 
-    func get(for key: BuilderKey, isCalledFromAChild: Bool) -> Builder?
+    func get<I, P>(for key: BuilderKey, isCalledFromAChild: Bool) -> Builder<I, P>?
 
-    func set<P, I>(scope: Scope, key: BuilderKey, builder: @escaping (() -> P) -> I)
+    func set<I, P>(_ buidler: Builder<I, P>, for key: BuilderKey)
 
     var parent: BuilderStoring? { get set }
 }
@@ -22,24 +22,32 @@ protocol BuilderStoring: AnyObject {
 
 extension BuilderStoring {
 
-    func get(for key: BuilderKey) -> Builder? {
+    func get<I, P>(for key: BuilderKey) -> Builder<I, P>? {
         return get(for: key, isCalledFromAChild: false)
     }
+
+    func set<I, P>(scope: Scope, for key: BuilderKey, body: @escaping Builder<I, P>.Body) {
+        set(Builder(scope: scope, body: body), for: key)
+    }
 }
 
 // MARK: - Store
 
 final class BuilderStore: BuilderStoring {
 
-    private var builders: [BuilderKey: Builder] = [:]
+    private var builders: [BuilderKey: AnyBuilder] = [:]
 
     weak var parent: BuilderStoring? = nil
 
-    func get(for key: BuilderKey, isCalledFromAChild: Bool) -> Builder? {
+    func get<I, P>(for key: BuilderKey, isCalledFromAChild: Bool) -> Builder<I, P>? {
 
-        guard let builder = builders[key] else {
+        guard let foundBuilder = builders[key] else {
             return parent?.get(for: key, isCalledFromAChild: true)
         }
+
+        guard let builder = foundBuilder as? Builder<I, P> else {
+            fatalError("Found a builder (\(foundBuilder.self)) with an incorrect type \(Builder<I, P>.self).")
+        }
 
         if (isCalledFromAChild && builder.scope.allowsAccessFromChildren) || !isCalledFromAChild {
             return builder
@@ -48,7 +56,7 @@ final class BuilderStore: BuilderStoring {
         return parent?.get(for: key, isCalledFromAChild: true)
     }
 
-    func set<P, I>(scope: Scope, key: BuilderKey, builder: @escaping (() -> P) -> I) {
-        builders[key] = Builder(scope: scope, body: builder)
+    func set<I, P>(_ builder: Builder<I, P>, for key: BuilderKey) {
+        builders[key] = builder
     }
 }

Sources/WeaverDI/DependencyContainer.swift

@@ -45,51 +45,51 @@ extension DependencyContainer: DependencyResolver {
     public func resolve<S>(_ serviceType: S.Type, name: String? = nil) -> S {
         let key = BuilderKey(for: serviceType, name: name)
 
-        guard let builder = builders.get(for: key) else {
+        guard let builder: Builder<S, DependencyContainer> = builders.get(for: key) else {
             fatalError("\(DependencyContainer.self): Could not resolve \(key).")
         }
 
-        return builder.functor()({ self })
+        return builder.make()({ self })
     }
 
     public func resolve<S, P1>(_ serviceType: S.Type, name: String? = nil, parameter: P1) -> S {
         let key = BuilderKey(for: serviceType, name: name, parameterType: P1.self)
 
-        guard let builder = builders.get(for: key) else {
+        guard let builder: Builder<S, (DependencyContainer, P1)> = builders.get(for: key) else {
             fatalError("\(DependencyContainer.self): Could not resolve \(key).")
         }
 
-        return builder.functor()({ (self, parameter) })
+        return builder.make()({ (self, parameter) })
     }
 
     public func resolve<S, P1, P2>(_ serviceType: S.Type, name: String? = nil, parameters p1: P1, _ p2: P2) -> S {
         let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self)
 
-        guard let builder = builders.get(for: key) else {
+        guard let builder: Builder<S, (DependencyContainer, P1, P2)> = builders.get(for: key) else {
             fatalError("\(DependencyContainer.self): Could not resolve \(key).")
         }
 
-        return builder.functor()({ (self, p1, p2) })
+        return builder.make()({ (self, p1, p2) })
     }
 
     public func resolve<S, P1, P2, P3>(_ serviceType: S.Type, name: String? = nil, parameters p1: P1, _ p2: P2, _ p3: P3) -> S {
         let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self, P3.self)
 
-        guard let builder = builders.get(for: key) else {
+        guard let builder: Builder<S, (DependencyContainer, P1, P2, P3)> = builders.get(for: key) else {
             fatalError("\(DependencyContainer.self): Could not resolve \(key).")
         }
 
-        return builder.functor()({ (self, p1, p2, p3) })
+        return builder.make()({ (self, p1, p2, p3) })
     }
 
     public func resolve<S, P1, P2, P3, P4>(_ serviceType: S.Type, name: String? = nil, parameters p1: P1, _ p2: P2, _ p3: P3, _ p4: P4) -> S {
         let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self, P3.self, P4.self)
 
-        guard let builder = builders.get(for: key) else {
+        guard let builder: Builder<S, (DependencyContainer, P1, P2, P3, P4)> = builders.get(for: key) else {
             fatalError("\(DependencyContainer.self): Could not resolve \(key).")
         }
 
-        return builder.functor()({ (self, p1, p2, p3, p4) })
+        return builder.make()({ (self, p1, p2, p3, p4) })
     }
 }
 
@@ -108,39 +108,39 @@ extension DependencyContainer {
         public func register<S>(_ serviceType: S.Type, scope: Scope, name: String? = nil, builder: @escaping (DependencyContainer) -> S) {
             let key = BuilderKey(for: serviceType, name: name)
 
-            builders.set(scope: scope, key: key) { (parameter: () -> (DependencyContainer)) -> S in
+            builders.set(scope: scope, for: key) { (parameter: () -> (DependencyContainer)) -> S in
                 return builder(parameter())
             }
         }
 
         public func register<S, P1>(_ serviceType: S.Type, scope: Scope, name: String? = nil, builder: @escaping (DependencyContainer, P1) -> S) {
             let key = BuilderKey(for: serviceType, name: name, parameterType: P1.self)
 
-            builders.set(scope: scope, key: key) { (parameters: () -> (DependencyContainer, P1)) -> S in
+            builders.set(scope: scope, for: key) { (parameters: () -> (DependencyContainer, P1)) -> S in
                 return builder(parameters().0, parameters().1)
             }
         }
 
         public func register<S, P1, P2>(_ serviceType: S.Type, scope: Scope, name: String? = nil, builder: @escaping (DependencyContainer, P1, P2) -> S) {
             let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self)
 
-            builders.set(scope: scope, key: key) { (parameters: () -> (DependencyContainer, P1, P2)) -> S in
+            builders.set(scope: scope, for: key) { (parameters: () -> (DependencyContainer, P1, P2)) -> S in
                 return builder(parameters().0, parameters().1, parameters().2)
             }
         }
 
         public func register<S, P1, P2, P3>(_ serviceType: S.Type, scope: Scope, name: String? = nil, builder: @escaping (DependencyContainer, P1, P2, P3) -> S) {
             let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self, P3.self)
 
-            builders.set(scope: scope, key: key) { (parameters: () -> (DependencyContainer, P1, P2, P3)) -> S in
+            builders.set(scope: scope, for: key) { (parameters: () -> (DependencyContainer, P1, P2, P3)) -> S in
                 return builder(parameters().0, parameters().1, parameters().2, parameters().3)
             }
         }
 
         public func register<S, P1, P2, P3, P4>(_ serviceType: S.Type, scope: Scope, name: String? = nil, builder: @escaping (DependencyContainer, P1, P2, P3, P4) -> S) {
             let key = BuilderKey(for: serviceType, name: name, parameterTypes: P1.self, P2.self, P3.self, P4.self)
 
-            builders.set(scope: scope, key: key) { (parameters: () -> (DependencyContainer, P1, P2, P3, P4)) -> S in
+            builders.set(scope: scope, for: key) { (parameters: () -> (DependencyContainer, P1, P2, P3, P4)) -> S in
                 return builder(parameters().0, parameters().1, parameters().2, parameters().3, parameters().4)
             }
         }