难以理解"泛型"的例子

Question

我正在阅读一本试图用C#理解泛型的书,我遇到了一个我不明白的例子.这是示例代码.

using System;

public class Printer
{
  public void Print<T>(T argument)
  {
    Console.WriteLine(argument.ToString());
  }

  static void Main(string[] arguments)
  {
    Printer printer = new Printer();
    printer.Print<string>("Hello, World");
    Console.WriteLine("Done");
    Console.ReadKey();
  }
}

令我困惑的是Print方法的论点.我理解在处理诸如的集合时使用泛型类型占位符List<T>.但是我不明白的是如何<T>使用方法？代码只是说传递给Print()方法的参数类型在设计时才知道,可能是什么？有人可以帮我解读一下吗？谢谢.

Answer 1

通过使用泛型类型声明方法,可以使方法更加灵活,因为它可以处理您选择的任何类型的变量,包括基本类型(除非您指定where T : class当然).

另一个非常常见的例子更好地说明了泛型方法的一种用法是一种Swap<T>(T, T)方法:

/* 
 * The ref keywords mean "pass by reference" i.e. modify the variables as they
 * were passed into the method.
 *
 * The <T> in the signature tells the compiler that T is a generic type, in case
 * the class itself doesn't already declare T a generic type.
 */
public void Swap<T>(ref T x, ref T y)
{
    // Tells the compiler that temp should be of the same type as x and y,
    // regardless of what type T may be
    T temp = x;
    x = y;
    y = temp;
}

int x = 3, y = 6;
Swap<int>(ref x, ref y);
Console.WriteLine(x + " " + y);

char a = 'a', b = 'b';
Swap<char>(ref a, ref b);
Console.WriteLine(a + " " + b);