SparkyTools.DependencyProvider 1.2.1

SparkyTools.DependencyProvider

see also:

• the rest of the "Sparky suite" of .NET utilities and test helpers

Ludicrously lightweight dependency wrapper/provider to improve testability of classes that use dependencies that aren't easily mockable (e.g. System.DateTime):

using SparkyTools.DependencyProvider;

    public class Foo
    {
        private readonly IBar _bar;
        private readonly DependencyProvider<DateTime> _currentTimeProvider;
       
        public Foo(IBar bar, DependencyProvider<DateTime> currentTimeProvider) 
        {
            _bar = bar;
            _getDate = currentTimeProvider;
        }
       
        public void DoSomethingWithBazAndDate()
        {
            _bar.DoSomethingWithDate(_currentTimeProvider.GetValue());
        }
    }

The DependencyProvider.GetValue() function provides a value to the class.

A DependencyProvider instance can be created:

• via a "callback function" constructor parameter:

  var realTimeProvider = new DependencyProvider<DateTime>(() => DateTime.Now);
  var fakeTimeProvider = new DependencyProvider<DateTime>(() => new DateTime(2018, 7, 4, 15, 32, 00));
  

• via the static Create(callbackFunction) method:

  var realTimeProvider = DependencyProvider.Create(() => DateTime.Now);
  var fakeTimeProvider = DependencyProvider.Create(() => new DateTime(2018, 7, 4, 15, 32, 00));
  

• via a static value constructor parameter:

  var realTimeProvider = new DependencyProvider<DateTime>(DateTime.Now);
  var fakeTimeProvider = new DependencyProvider<DateTime>(new DateTime(2018, 7, 4, 15, 32, 00));
  

• via the static Create(staticValue) method:

  var realTimeProvider = DependencyProvider.Create(DateTime.Now);
  var fakeTimeProvider = DependencyProvider.Create(new DateTime(2018, 7, 4, 15, 32, 00));
  

• via implicit conversion:

  DependencyProvider<DateTime> realTimeProvider = DateTime.Now(); 
  DependencyProvider<DateTime> fakeTimeProvider = new DateTime(2018, 7, 4, 15, 32, 00);
  

The implicit conversion option makes for very nice, terse syntax when declared inline for the constructor of a class using DependencyProvider, e.g.:

    public class Foo
    {
        public Foo(IBar bar, DependencyProvider<DateTime> currentTimeProvider) { }
    }

    ...
    // implicit conversion:
    var fooWithRealTime = new Foo(bar, DateTime.Now());
    var fooWithFakeTime = new Foo(bar, new DateTime(2018, 7, 4, 15, 32, 00));

    // other syntaxes:
    var fooWithRealTime2 = new Foo(bar, DependencyProvider.Create(DateTime.Now));
    var foowithFakeTime2 = new Foo(bar, new DependencyProvider<DateTime>(new DateTime(2018, 7, 4, 15, 32, 00)));

The DependencyProvider.Static() method tells the provider to cache the first value returned by GetValue() and return that same value for all subsequent calls:

    var startTimeProvider = DependencyProvider.Create(() => DateTime.Now).Static();

DependencyProviders created via the static value constructor and Create(staticValue) methods get their static values when constructed. Providers that aren't constructed statically but are "dotted" with .Static() are "lazy". They don't get retrieve their value until the first GetValue() call.