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| using System; | |
| using System.Linq; | |
| using System.Reflection; | |
| namespace NullObjectDesignPattern | |
| { | |
| class Program | |
| { | |
| static void Main(string[] args) | |
| { | |
| // parameterless -- falls back to default dog | |
| var dogFactory = new Factory<Dog>(new Dog { Name = "Tommy" }); | |
| var dog1 = dogFactory.Create("Bruno"); | |
| Console.WriteLine(dog1.Name); | |
| // parameterless -- overrides default dog | |
| var dog2 = dogFactory.Create(); | |
| Console.WriteLine(dog2.Name); | |
| // parameterless -- falls back to default Cat | |
| var catFactory = new Factory<Cat>(new Cat("Lisa")); | |
| var cat1 = catFactory.Create(); | |
| Console.WriteLine(cat1.Name); | |
| // parameterized -- overrides default Cat | |
| var cat2 = catFactory.Create("Polly"); | |
| Console.WriteLine(cat2.Name); | |
| Console.ReadKey(); | |
| } | |
| } | |
| class Factory<T> where T: class | |
| { | |
| private T _defaultValue = default(T); | |
| public Factory(T defaultValue = default(T)) | |
| { | |
| _defaultValue = defaultValue; | |
| } | |
| public T Create(params object[] args) | |
| { | |
| return TryCreate(args) ?? _defaultValue; | |
| } | |
| protected virtual T TryCreate(params object[] args) | |
| { | |
| var matchingCtor = (from ctor in typeof(T).GetConstructors() | |
| let parameters = ctor.GetParameters() | |
| let i = 0 | |
| where parameters.Length == args.Length | |
| where parameters.AndArgumentTypesAreSame(args) | |
| select ctor).FirstOrDefault(); | |
| if (matchingCtor == null) return null; | |
| return matchingCtor.Invoke(args) as T; | |
| } | |
| } | |
| public static class Extensions | |
| { | |
| public static bool AndArgumentTypesAreSame(this ParameterInfo[] parameterInfoArray, object[] argumentArray) | |
| { | |
| if (parameterInfoArray != null && argumentArray != null && parameterInfoArray.Length == argumentArray.Length) | |
| { | |
| for(int i = 0; i < parameterInfoArray.Length; i++) | |
| { | |
| if (parameterInfoArray[i].ParameterType != argumentArray[i].GetType()) | |
| return false; | |
| } | |
| return true; | |
| } | |
| return false; | |
| } | |
| } | |
| class Dog | |
| { | |
| public string Name { get; set; } = "Woofy"; | |
| } | |
| class Cat | |
| { | |
| public string Name { get; set; } | |
| public Cat(string name) | |
| { | |
| Name = name; | |
| } | |
| } | |
| } |
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