In Objective-C instance data can be public, protected or private. For example:
#interface Foo : NSObject
{
#public
int x;
#protected:
int y;
#private:
int z;
}
-(int) apple;
-(int) pear;
-(int) banana;
#end
I haven't found any mention of access modifiers in the Swift reference. Is it possible to limit the visibility of data in Swift?
As of Swift 3.0.1, there are 4 levels of access, described below from the highest (least restrictive) to the lowest (most restrictive).
1. open and public
Enable an entity to be used outside the defining module (target). You typically use open or public access when specifying the public interface to a framework.
However, open access applies only to classes and class members, and it differs from public access as follows:
public classes and class members can only be subclassed and overridden within the defining module (target).
open classes and class members can be subclassed and overridden both within and outside the defining module (target).
// First.framework – A.swift
open class A {}
// First.framework – B.swift
public class B: A {} // ok
// Second.framework – C.swift
import First
internal class C: A {} // ok
// Second.framework – D.swift
import First
internal class D: B {} // error: B cannot be subclassed
2. internal
Enables an entity to be used within the defining module (target). You typically use internal access when defining an app’s or a framework’s internal structure.
// First.framework – A.swift
internal struct A {}
// First.framework – B.swift
A() // ok
// Second.framework – C.swift
import First
A() // error: A is unavailable
3. fileprivate
Restricts the use of an entity to its defining source file. You typically use fileprivate access to hide the implementation details of a specific piece of functionality when those details are used within an entire file.
// First.framework – A.swift
internal struct A {
fileprivate static let x: Int
}
A.x // ok
// First.framework – B.swift
A.x // error: x is not available
4. private
Restricts the use of an entity to its enclosing declaration. You typically use private access to hide the implementation details of a specific piece of functionality when those details are used only within a single declaration.
// First.framework – A.swift
internal struct A {
private static let x: Int
internal static func doSomethingWithX() {
x // ok
}
}
A.x // error: x is unavailable
Swift 4 / Swift 5
As per mentioned in the Swift Documentation - Access Control, Swift has 5 Access Controls:
open and public: can be accessed from their module's entities and any module's entities that imports the defining module.
internal: can only be accessed from their module's entities. It is the default access level.
fileprivate and private: can only be accessed in limited within a limited scope where you define them.
What is the difference between open and public?
open is the same as public in previous versions of Swift, they allow classes from other modules to use and inherit them, i.e: they can be subclassed from other modules. Also, they allow members from other modules to use and override them. The same logic goes for their modules.
public allow classes from other module to use them, but not to inherit them, i.e: they cannot be subclassed from other modules. Also, they allow members from other modules to use them, but NOT to override them. For their modules, they have the same open's logic (they allow classes to use and inherit them; They allow members to use and override them).
What is the difference between fileprivate and private?
fileprivate can be accessed from the their entire files.
private can only be accessed from their single declaration and to extensions of that declaration that are in the same file; For instance:
// Declaring "A" class that has the two types of "private" and "fileprivate":
class A {
private var aPrivate: String?
fileprivate var aFileprivate: String?
func accessMySelf() {
// this works fine
self.aPrivate = ""
self.aFileprivate = ""
}
}
// Declaring "B" for checking the abiltiy of accessing "A" class:
class B {
func accessA() {
// create an instance of "A" class
let aObject = A()
// Error! this is NOT accessable...
aObject.aPrivate = "I CANNOT set a value for it!"
// this works fine
aObject.aFileprivate = "I CAN set a value for it!"
}
}
What are the differences between Swift 3 and Swift 4 Access Control?
As mentioned in the SE-0169 proposal, the only refinement has been added to Swift 4 is that the private access control scope has been expanded to be accessible from extensions of that declaration in the same file; For instance:
struct MyStruct {
private let myMessage = "Hello World"
}
extension MyStruct {
func printMyMessage() {
print(myMessage)
// In Swift 3, you will get a compile time error:
// error: 'myMessage' is inaccessible due to 'private' protection level
// In Swift 4 it should works fine!
}
}
So, there is no need to declare myMessage as fileprivate to be accessible in the whole file.
When one talks about making a "private method" in Swift or ObjC (or ruby or java or…) those methods aren't really private. There's no actual access control around them. Any language that offers even a little introspection lets developers get to those values from outside the class if they really want to.
So what we're really talking about here is a way to define a public-facing interface that merely presents the functionality we want it to, and "hides" the rest that we consider "private".
The Swift mechanism for declaring interfaces is the protocol, and it can be used for this purpose.
protocol MyClass {
var publicProperty:Int {get set}
func publicMethod(foo:String)->String
}
class MyClassImplementation : MyClass {
var publicProperty:Int = 5
var privateProperty:Int = 8
func publicMethod(foo:String)->String{
return privateMethod(foo)
}
func privateMethod(foo:String)->String{
return "Hello \(foo)"
}
}
Remember, protocols are first-class types and can be used anyplace a type can. And, when used this way, they only expose their own interfaces, not those of the implementing type.
Thus, as long as you use MyClass instead of MyClassImplementation in your parameter types, etc. it should all just work:
func breakingAndEntering(foo:MyClass)->String{
return foo.privateMethod()
//ERROR: 'MyClass' does not have a member named 'privateMethod'
}
There are some cases of direct assignment where you have to be explicit with type instead of relying on Swift to infer it, but that hardly seems a deal breaker:
var myClass:MyClass = MyClassImplementation()
Using protocols this way is semantic, reasonably concise, and to my eyes looks a lot like the Class Extentions we've been using for this purpose in ObjC.
As far as I can tell, there are no keywords 'public', 'private' or 'protected'. This would suggest everything is public.
However Apple may be expecting people to use “protocols” (called interfaces by the rest of the world) and the factory design pattern to hide details of the implementation type.
This is often a good design pattern to use anyway; as it lets you change your implementation class hierarchy, while keeping the logical type system the same.
Using a combination of protocols, closures, and nested/inner classes, it's possible to use something along the lines of the module pattern to hide information in Swift right now. It's not super clean or nice to read but it does work.
Example:
protocol HuhThing {
var huh: Int { get set }
}
func HuhMaker() -> HuhThing {
class InnerHuh: HuhThing {
var innerVal: Int = 0
var huh: Int {
get {
return mysteriousMath(innerVal)
}
set {
innerVal = newValue / 2
}
}
func mysteriousMath(number: Int) -> Int {
return number * 3 + 2
}
}
return InnerHuh()
}
HuhMaker()
var h = HuhMaker()
h.huh // 2
h.huh = 32
h.huh // 50
h.huh = 39
h.huh // 59
innerVal and mysteriousMath are hidden here from outside use and attempting to dig your way into the object should result in an error.
I'm only part of the way through my reading of the Swift docs so if there's a flaw here please point it out, would love to know.
As of Xcode 6 beta 4, Swift has access modifiers. From the release notes:
Swift access control has three access levels:
private entities can only be accessed from within the source file where they are defined.
internal entities can be accessed anywhere within the target where they are defined.
public entities can be accessed from anywhere within the target and from any other context that imports the current target’s module.
The implicit default is internal, so within an application target you can leave access modifiers off except where you want to be more restrictive. In a framework target (e.g. if you're embedding a framework to share code between an app and an sharing or Today view extension), use public to designate API you want to expose to clients of your framework.
Swift 3.0 provides five different access controls:
open
public
internal
fileprivate
private
Open access and public access enable entities to be used within any source file from their defining module, and also in a
source file from another module that imports the defining module. You
typically use open or public access when specifying the public
interface to a framework.
Internal access enables entities to be used within any source file from their defining module, but not in any source file outside of that
module. You typically use internal access when defining an app’s or a
framework’s internal structure.
File-private access restricts the use of an entity to its own defining source file. Use file-private access to hide the
implementation details of a specific piece of functionality when those
details are used within an entire file.
Private access restricts the use of an entity to the enclosing declaration. Use private access to hide the implementation details of
a specific piece of functionality when those details are used only
within a single declaration.
Open access is the highest (least restrictive) access level and private access is the lowest (most restrictive) access level.
Default Access Levels
All entities in your code (with a few specific exceptions) have a default access level of internal if you do not specify an explicit access level yourself. As a result, in many cases you do not need to specify an explicit access level in your code.
The release note on the topic:
Classes declared as public can no longer be subclassed outside of
their defining module, and methods declared as public can no longer be
overridden outside of their defining module. To allow a class to be
externally subclassed or a method to be externally overridden, declare
them as open, which is a new access level beyond public. Imported
Objective-C classes and methods are now all imported as open rather
than public. Unit tests that import a module using an #testable import
will still be allowed to subclass public or internal classes as well
as override public or internal methods. (SE-0117)
More information & details :
The Swift Programming Language (Access Control)
In Beta 6, the documentation states that there are three different access modifiers:
Public
Internal
Private
And these three apply to Classes, Protocols, functions and properties.
public var somePublicVariable = 0
internal let someInternalConstant = 0
private func somePrivateFunction() {}
For more, check Access Control.
Now in beta 4, they've added access modifiers to Swift.
from Xcode 6 beta 4 realese notes:
Swift access control has three access levels:
private entities can only be accessed from within the source file where they are defined.
internal entities can be accessed anywhere within the target where they are defined.
public entities can be accessed from anywhere within the target and from any other context
that imports the current target’s module.
By default, most entities in a source file have internal access. This allows application developers
to largely ignore access control while allowing framework developers full control over a
framework's API.
Access control mechanisms as introduced in Xcode 6:
Swift provides three different access levels for entities within your code. These access levels are relative to the source file in which an entity is defined, and also relative to the module that source file belongs to.
Public access enables entities to be used within any source file from their defining module, and also in a source file from another module that imports the defining module. You typically use public access when specifying the public interface to a framework.
Internal access enables entities to be used within any source file from their defining module, but not in any source file outside of that module. You typically use internal access when defining an app’s or a framework’s internal structure.
Private access restricts the use of an entity to its own defining source file. Use private access to hide the implementation details of a specific piece of functionality.
Public access is the highest (least restrictive) access level and private access is the lowest (or most restrictive) access level.
Default accecss it internal, and does as such not need to be specified. Also note that the private specifier does not work on the class level, but on the source file level. This means that to get parts of a class really private you need to separate into a file of its own. This also introduces some interesting cases with regards to unit testing...
Another point to me made, which is commented upon in the link above, is that you can't 'upgrade' the access level. If you subclass something, you can restrict it more, but not the other way around.
This last bit also affects functions, tuples and surely other stuff in the way that if i.e. a function uses a private class, then it's not valid to have the function internal or public, as they might not have access to the private class. This results in a compiler warning, and you need to redeclare the function as a private function.
Swift 3 and 4 brought a lot of change also for the access levels of variables and methods. Swift 3 and 4 now has 4 different access levels, where open/public access is the highest (least restrictive) access level and private access is the lowest (most restrictive) access level:
private functions and members can only be accessed from within the scope of the entity itself (struct, class, …) and its extensions (in Swift 3 also the extensions were restricted)
fileprivate functions and members can only be accessed from within the source file where they are declared.
internal functions and members (which is the default, if you do not explicitly add an access level key word) can be accessed anywhere within the target where they are defined. Thats why the TestTarget doesn't have automatically access to all sources, they have to be marked as accessible in xCode's file inspector.
open or public functions and members can be accessed from anywhere within the target and from any other context that imports the current target’s module.
Interesting:
Instead of marking every single method or member as "private", you can cover some methods (e.g. typically helper functions) in an extension of a class / struct and mark the whole extension as "Private".
class foo { }
private extension foo {
func somePrivateHelperFunction01() { }
func somePrivateHelperFunction02() { }
func somePrivateHelperFunction03() { }
}
This can be a good idea, in order to get better maintainable code. And you can easily switch (e.g. for unit testing) to non-private by just changing one word.
Apple documentation
For Swift 1-3:
No, it's not possible. There aren't any private/protected methods and variables at all.
Everything is public.
Update
Since Swift 4, it's possible see other answers in this thread
One of the options you could use is to wrap the instance creation into a function and supply the appropriate getters and setters in a constructor:
class Counter {
let inc: () -> Int
let dec: () -> Int
init(start: Int) {
var n = start
inc = { ++n }
dec = { --n }
}
}
let c = Counter(start: 10)
c.inc() // 11
c.inc() // 12
c.dec() // 11
The language grammar does not have the keywords 'public', 'private' or 'protected'. This would suggest everything is public. Of course, there could be some alternative method of specifying access modifiers without those keywords but I couldn't find it in the language reference.
Hopefully to save some time for those who want something akin to protected methods:
As per other answers, swift now provides the 'private' modifier - which is defined file-wise rather than class-wise such as those in Java or C# for instance. This means that if you want protected methods, you can do it with swift private methods if they are in the same file
Create a base class to hold 'protected' methods (actually private)
Subclass this class to use the same methods
In other files you cannot access the base class methods, even when you subclass either
e.g. File 1:
class BaseClass {
private func protectedMethod() {
}
}
class SubClass : BaseClass {
func publicMethod() {
self.protectedMethod() //this is ok as they are in same file
}
}
File 2:
func test() {
var a = BaseClass()
a.protectedMethod() //ERROR
var b = SubClass()
b.protectedMethod() //ERROR
}
class SubClass2 : BaseClass {
func publicMethod() {
self.protectedMethod() //ERROR
}
}
till swift 2.0 there were only three access level [Public, internal, private]
but in swift 3.0 apple added two new access level which are [ Open, fileType ] so
now in swift 3.0 there are 5 access level
Here I want to clear the role of these two access level
1. Open: this is much similar to Public but the only difference is that the Public
can access the subclass and override, and Open access level can not access that this image is taken from Medium website and this describe the difference between open and public access
Now to second new access level
2. filetype is bigger version of private or less access level than internal
The fileType can access the extended part of the [class, struct, enum]
and private can not access the extended part of code it can only access the
lexical scope
this image is taken from Medium website and this describe the difference between fileType and Private access level
Related
I'm trying to get an understanding of which concrete types are providing the implementations of interfaces in an IOC (dependency injection) container. My implementation works fine when there are no delegates involved. However, I'm having trouble when a delegate method is passed as the type factory, as I can't get Mono.Cecil to give me the concrete type or a method reference to the factory back. I'm specifically in this case trying to build a component that can work with the IServiceCollection container for .Net ASP.Net REST APIs. I've created a 'minimised' set of code below to make it easy to explain the problem.
Consider the following C# code:
interface IServiceProvider {}
interface IServiceCollection {}
class ServicesCollection : IServiceCollection {}
interface IMongoDBContext {}
class MongoDBContext : IMongoDBContext
{
public MongoDBContext(string configName) {}
}
static class Extensions
{
public static IServiceCollection AddSingleton<TService>(this IServiceCollection services, Func<IServiceProvider, TService> implementationFactory) where TService : class
{
return null;
}
}
class Foo
{
void Bar()
{
IServiceCollection services = new ServicesCollection();
services.AddSingleton<IMongoDBContext>(s => new MongoDBContext("mongodbConfig"));
}
}
When successfully locating the 'services.AddSingleton' as a MethodReference, I'm unable to see any reference to the MongoDBContext class, or its constructor. When printing all the instructions .ToString() I also cannot seem to see anything in the IL - I do see the numbered parameter as !!0, but that doesn't help if I can't resolve it to a type or to the factory method.
Does anyone have any ideas on how to solve this?
Most likely your code is looking in the wrong place.
C# compiler will try to cache the conversion of lambda expression -> delegate.
if you look in sharplab.io you'll see that the compiler is emitting an inner class '<>c' inside your Foo class and in that class it emits the method '<Bar>b__0_0' that will be passed as the delegate (see opcode ldftn).
I don't think there's an easy, non fragile way to find that method.
That said, one option would be to:
Find the AddSingleton() method call
From there start going back to the previous instructions trying to identify which one is pushing the value consumed in 1 (the safest way to do that would be to consider how each instruction you are visiting changes the stack). In the code I've linked, it would be IL_0021 (a dup) of Bar() method.
From there, do something similar to 2, but now looking for the instruction that pushes the method reference (a ldftn) used by the ctor of Func<T, R>; in the code linked, it would be IL_0016.
Now you can inspect the body (in the code linked, Foo/'<>c'::'<Bar>b__0_0')
Note that this implementation has some holes though; for instance, if you call AddSingleton() with a variable/parameter/field as I've done (services.AddSingleton(_func);) you'll need to chase the initialization of that to find the referenced method.
Interestingly, at some point Cecil project did support flow analysis (https://github.com/mono/cecil-old/tree/master/flowanalysis).
If you have access to the source code, I think it would be easier to use Roslyn to analyze it (instead of analyzing the assembly).
For those of you that are familiar with the building of the Symfony container, do you know what is the differences (if any) between
Tagged service Collector using a Compiler pass
Tagged service Collector using the supported shortcut
Service Locator especially, one that collects services by tags
Specifically, I am wondering about whether these methods differ on making these collected services available sooner or later in the container build process. Also I am wondering about the ‘laziness’ of any of them.
It can certainly be confusing when trying to understand the differences. Keep in mind that the latter two approaches are fairly new. The documentation has not quite caught up. You might actually consider making a new project and doing some experimenting.
Approach 1 is basically an "old school" style. You have:
class MyCollector {
private $handlers = [];
public function addHandler(MyHandler $hamdler) {
$handlers[] = $handler;
# compiler pass
$myCollectorDefinition->addMethodCall('addHandler', [new Reference($handlerServiceId)]);
So basically the container will instantiate MyCollector then explicitly call addHandler for each handler service. In doing so, the handler services will be instantiated unless you do some proxy stuff. So no lazy creation.
The second approach provides a somewhat similar capability but uses an iterable object instead of a plain php array:
class MyCollection {
public function __construct(iterable $handlers)
# services.yaml
App\MyCollection:
arguments:
- !tagged_iterator my.handler
One nice thing about this approach is that the iterable actually ends up connecting to the container via closures and will only instantiate individual handlers when they are actually accessed. So lazy handler creation. Also, there are some variations on how you can specify the key.
I might point out that typically you auto-tag your individual handlers with:
# services.yaml
services:
_instanceof:
App\MyHandlerInterface:
tags: ['my.handler']
So no compiler pass needed.
The third approach is basically the same as the second except that handler services can be accessed individually by an index. This is useful when you need one out of all the possible services. And of course the service selected is only created when you ask for it.
class MyCollection {
public function __construct(ServiceLocator $locator) {
$this->locator = $locator;
}
public function doSomething($handlerKey) {
/** #var MyHandlerInterface $handler */
$handler = $serviceLocator->get($handlerKey);
# services.yaml
App\MyCollection:
arguments: [!tagged_locator { tag: 'app.handler', index_by: 'key' }]
I should point out that in all these cases, the code does not actually know the class of your handler service. Hence the var comment to keep the IDE happy.
There is another approach which I like in which you make your own ServiceLocator and then specify the type of object being located. No need for a var comment. Something like:
class MyHandlerLocator extends ServiceLocator
{
public function get($id) : MyHandlerInterface
{
return parent::get($id);
}
}
The only way I have been able to get this approach to work is a compiler pass. I won't post the code here as it is somewhat outside the scope of the question. But in exchange for a few lines of pass code you get a nice clean custom locator which can also pick up handlers from other bundles.
For example, let's say I have an interface 'IFeed' and two concrete types ('Feed1' and 'Feed2') that implement this interface. Now let's say I have a 'FeedManager' type that takes multiple parameters that will get resolved dynamically, two of which are of type 'IFeed' and I'd like both concrete type to be injected via constructor injection, not via manual resolve (I only use resolve once at the composition root). I have a feeling that I should be using a factory but I wanted to see what the proper way of doing this might be. Many thanks in advance.
If you want ALL implementations of IFeed, you can use array syntax in your constructor and then nothing special is needed at type registration time.
container.RegisterType<IFeedManager, FeedManager>();
container.RegisterType<IFeed, FeedA>("FeedA"); // The name doesn't matter
container.RegisterType<IFeed, FeedB>("FeedB"); // The name doesn't matter
Then the manager constructor...
public FeedManager(IFeed[] feeds) {...}
or if you want to add a little flare for calling the constructor directly...
public FeedManager(params IFeed[] feeds) {...}
Assuming you want to determine the actual concrete instances at runtime, you need to use named type registrations and then tell unity which one you want. So, use a factory method to construct the types required and pass those in as parameter overrides. Unity will use the overrides and resolve any remaining dependencies.
// register the types using named registrations
container.RegisterType<IFeedManager,FeedManager>()
container.RegisterType<IFeed, Feed1>("Feed1")
container.RegisterType<IFeed, Feed2>("Feed2")
Assuming your feed manager has the following named constructor parameters
class FeedManager : IFeedManager
{
public FeedManager (IFeed Feed1, IFeed Feed2, string someOtherDependency)
{
}
}
and create your feed manager:
static IFeedManager CreateFeedManager()
{
ParameterOverride feed1 = new ParameterOverride("Feed1"
,_container.Resolve<IFeed>("feed1"));
ParameterOverride feed2 = new DependencyOverride("Feed2"
,_container.Resolve<IFeed>("feed2"));
IFeedManager = _container.Resolve<IFeedManager>(feed1,feed2)
return IFeedManager;
}
Obviously this is overly simplified, but you you insert your own logic to determine which instance is to be resolved and then injected for each of the IFeed instances required by the FeedManager.
With Unity you would do this like so:
container.RegisterType<IFeed, Feed1>("Feed1");
container.RegisterType<IFeed, Feed2>("Feed2");
container.RegisterType<FeedManager>(new InjectionConstructor(new ResolvedParameter<IFeed>("Feed1"),
new ResolvedParameter<IFeed>("Feed2")));
This has now configured Unity so that when it needs to resolve a FeedManager, it will resolve Feed1 for the first parameter and Feed2 for the second parameter.
Is it possible to make unity try all defined constructors starting with the one with most arguments down to the least specific one (the default constructor)?
Edit
What I mean:
foreach (var constructor in concrete.GetConstructorsOrderByParameterCount())
{
if(CanFulfilDependencies(constructor))
{
UseConstructor(constructor);
break;
}
}
I don't want Unity to only try the constructor with most parameters. I want it to continue trying until it finds a suitable constructor. If Unity doesn't provide this behavior by default, is it possible to create an extension or something to be able to do this?
Edit 2
I got a class with two constructors:
public class MyConcrete : ISomeInterface
{
public MyConcrete (IDepend1 dep, IDepend2 dep2)
{}
public MyConcrete(IDepend1 dep)
{}
}
The class exists in a library which is used by multiple projects. In this project I want to use second constructor. But Unity stops since it can't fulfill the dependencies by the first constructor. And I do not want to change the class since the first constructor is used by DI in other projects.
Hence the need for Unity to try resolving all constructors.
Unity will choose the constructor with the most parameters unless you explicitly tag a constructor with the [InjectionConstructor] attribute which would then define the constructor for Unity to use.
When you state a suitable constructor; that is somewhat contingent on the environment. If for instance you always want to guarantee that a certain constructor is used when making use of Unity use the attribute mentioned previously, otherwise explicitly call the constructor you want to use.
What would be the point of Unity "trying" all constructors? It's purpose is to provide an instance of a type in a decoupled manner. Why would it iterate through the constructors if any constructor will create an instance of the type?
EDIT:
You could allow the constructor with the most params to be used within the project that does not have a reference to that type within its container by making use of a child container. This will not force the use of the constructor with a single param but it will allow the constructor with 2 params to work across the projects now.
You could also switch to using the single constructor across the board and force the other interface in via another form of DI (Property Injection), not Constructor Injection...therefore the base is applicable across the projects which would make more sense.
ASP.NET 3.5
Classes throughout our solution referenced ConfigurationManater.AppSettings[""] to get appSettings (from web.config).
We decided we weren't happy with that. Folks were mistyping appSetting key names in code (which compiled fine), and it was cumbersome to track usages. And then there's the duplicated strings throughout the codebase as you reference the same appSettings all over the place.
So, we decided that only one class would be allowed to reference the ConfigurationManager, and the rest of the solution would reference that class when it needed the value of a certain appSetting. ConfigurationManater.AppSettings[""] was static, so we exposed a bunch of static read-only properties off of our single Settings class.
public class Settings {
public static string Foo {
get {
return ConfigurationManager.AppSettings["Foo"];
}
}
}
That worked pretty well, until we needed to mock the settings in our tests. We created an interface to enable our mocking (was this a mistake of any kind?).
public interface ISettings {
string Foo {
get;
set;
}
}
public class Settings : ISettings {
public string Foo {
get {
return ConfigurationManager.AppSettings["Foo"];
}
}
}
And now we're injecting the ISettings instance as a dependency of the objects which use settings values (the class/interface are in a project that everyone can reference without problems).
In places where we can't inject an existing instance (e.g. Global.asax), we construct a new instance into a static field.
Given all of that, what would you recommend we change, and why?
Using an interface to represent configuration is a good idea. But your implementation looks a little off.
Joshua Flanagan wrote about writing application configuration code in a way that specific configuration sections can be injected into your code. This is a good idea, as it really decouples your code from worrying about details behind configuration. Have a read.
I think this will address the issue you are having re. testability.