C# 泛型特化
阿新 • • 發佈:2017-06-20
但是 data load max fim not str wrap lock
C# 泛型不是 C++ 的模板類,並不支持特化和偏特化,但是使用一些技巧可以在一定程度上達到相同的目的。
原文是 po 在 stackoverflow 上的一個回答:A: Generic indexer overload specialization
一、泛型方法的特化
使用一個非泛型 helper 類和一個內嵌的泛型類可以實現對泛型方法的特化。
1 internal static class IndexerImpl //non-generic static helper class 2 { 3 private static T IndexerDefaultImpl<T>(inti) => default(T); //default implementation 4 5 private static T IndexerImpl2<T>(int i) => default(T); //another implementation for short/int/long 6 7 private static string IndexerForString(int i) => (i * i).ToString(); //specialization for T=string 8 private staticDateTime IndexerForDateTime(int i) => new DateTime(i * i * i); //specialization for T=DateTime 9 10 static IndexerImpl() //install the specializations 11 { 12 Specializer<string>.Fun = IndexerForString; 13 Specializer<DateTime>.Fun = IndexerForDateTime;14 15 Specializer<short>.Fun = IndexerImpl2<short>; 16 Specializer<int>.Fun = IndexerImpl2<int>; 17 Specializer<long>.Fun = IndexerImpl2<long>; 18 } 19 20 internal static class Specializer<T> //specialization dispatcher 21 { 22 internal static Func<int, T> Fun; 23 internal static T Call(int i) 24 => null != Fun 25 ? Fun(i) 26 : IndexerDefaultImpl<T>(i); 27 } 28 } 29 30 public class YourClass<T> 31 { 32 public T this[int i] => IndexerImpl.Specializer<T>.Call(i); 33 }
如果需要傳入實例對返回結果進行計算,可以增加一個參數:
1 internal static class IndexerImpl //non-generic static helper class 2 { 3 private static T IndexerDefaultImpl<T>(int i, YourClass<T> yourClass) => default(T); //default implementation 4 5 private static T IndexerImpl2<T>(int i, YourClass<T> yourClass) => default(T); //another implementation for short/int/long 6 7 private static string IndexerForString<T>(int i, YourClass<T> yourClass) => (i * i).ToString(); //specialization for T=string 8 private static DateTime IndexerForDateTime<T>(int i, YourClass<T> yourClass) => new DateTime(i * i * i); //specialization for T=DateTime 9 10 static IndexerImpl() //install the specializations 11 { 12 Specializer<string>.Fun = IndexerForString; 13 Specializer<DateTime>.Fun = IndexerForDateTime; 14 15 Specializer<short>.Fun = IndexerImpl2; 16 Specializer<int>.Fun = IndexerImpl2; 17 Specializer<long>.Fun = IndexerImpl2; 18 } 19 20 internal static class Specializer<T> //specialization dispatcher 21 { 22 internal static Func<int, YourClass<T>, T> Fun; 23 internal static T Call(int i, YourClass<T> yourClass) 24 => null != Fun 25 ? Fun(i, yourClass) 26 : IndexerDefaultImpl(i, yourClass); 27 } 28 } 29 30 public class YourClass<T> 31 { 32 public T this[int i] => IndexerImpl.Specializer<T>.Call(i, this); 33 }
二、泛型方法的偏特化
偏特化也是差不多的做法,只不過幫助類變成了以不需要特化的類型構成的泛型類:
1 internal static class GetValueImpl<R, S> 2 { 3 private static T DefImpl<T>(R r, S s) => default(T); 4 private static int IntRet(R r, S s) => int.MaxValue; 5 6 internal static class Specializer<T> 7 { 8 internal static Func<R, S, T> Fun; 9 internal static T Call(R r, S s) => null != Fun ? Fun(r, s) : DefImpl<T>(r, s); 10 } 11 12 static GetValueImpl() 13 { 14 Specializer<int>.Fun = IntRet; 15 } 16 } 17 18 public class TestClass 19 { 20 public T GetValue<R, S, T>(R r, S s) => GetValueImpl<R, S>.Specializer<T>.Call(r, s); 21 }
以上代碼片段中,被偏特化的是 GetValue 方法中的 T 類型參數,當 T=int 的時候,實際被調用的方法就是 GetValueImpl.IntRet 方法,其他情況是 GetValueImpl.DefImpl 方法。
三、泛型類的特化
泛型類的特化沒有什麽好的方法,只能采用繼承特化類型泛型類的方式間接實現,並且將要特化處理的成員采用虛方法或者用 new 隱藏基類方法。
偏特化泛型類也可以采用差不多的方式實現。
具體做法可以參考 stackoverflow 上的這個答案:A: C# specialize generic class
C# 泛型特化