SparkyTools: DependencyProvider

part of the “SparkyTools” suite of .NET utility libraries

photo by Dan Machold

NuGet Package | Source Code

This NuGet package provides a ludicrously lightweight dependency wrapper/provider to improve testability of classes that use dependencies that aren’t easily mockable (e.g. System.DateTime):

using SparkyTools.DepndencyProvider;
...
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>(() => 
    DateTime.Parse("4/20/2018 4:20 PM"));

• via the static Create(callbackFunction) method:

var realTimeProvider = 
  DependencyProvider.Create(() => DateTime.Now);
var fakeTimeProvider = 
  DependencyProvider.Create(() => 
    DateTime.Parse("4/20/2018 4:20 PM"));

• via a static value constructor parameter:

var realTimeProvider = 
  new DependencyProvider<DateTime>(DateTime.Now);
var fakeTimeProvider = 
  new DependencyProvider<DateTime>(
    DateTime.Parse("4/20/2018 4:20 PM"));

• via the static Create(staticValue) method:

var realTimeProvider = 
  DependencyProvider.Create(DateTime.Now);
var fakeTimeProvider = 
  DependencyProvider.Create(
    DateTime.Parse("4/20/2018 4:20 PM"));

• via implicit conversion (thanks to David Kemp):

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.:

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

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.