在类型转换时常会遇到隐式转换和显式转换。那我们自己定义的类型要怎样去定义隐式转换和显式转换？我们来看一段代码

public class Rational{private Int32 _inner_int = 0;public Rational(){}public Rational(Int32 num){this._inner_int = num;}public Int32 ToInt32() { return this._inner_int; }// Implicitly constructs and returns a Rational from an Int32 public static implicit operator Rational(Int32 num){return new Rational(num);}// Explicitly returns an Int32 from a Rational public static explicit operator Int32(Rational r){return r.ToInt32();}public override string ToString(){//return base.ToString();String s = String.Format("{0}", this._inner_int);return s;}}

測试代码

  class Program{static void Main(string[] args){Rational r1 = 10;          Console.WriteLine(r1);       Int32 i = r1;     Console.WriteLine(i);       Console.ReadLine();}}

这时编辑会报错，见下图

从提示能够看到，是由于Int32 i=r1时缺少了显式转换。如今我们加入显示转换，改动后的代码及输出结果例如以下：

结果正常输出为10.

那为什么会这样呢？究其原因是在Rational转换成 Int32时，指定了explicit(显式的)，所以必需要指定转换类型Int32。假设将explicit换成implicit(隐式)，原来的代码将能够正常执行。

改动后的Rational

 public class Rational{private Int32 _inner_int = 0;public Rational(){}public Rational(Int32 num){this._inner_int = num;}public Int32 ToInt32() { return this._inner_int; }// Implicitly constructs and returns a Rational from an Int32 public static implicit operator Rational(Int32 num){return new Rational(num);}// Explicitly returns an Int32 from a Rational public static <span style="color:#ff0000;">implicit</span> operator Int32(Rational r){return r.ToInt32();}public override string ToString(){//return base.ToString();String s = String.Format("{0}", this._inner_int);return s;}}

測试代码及输出结果

可见explicit和implicit影响着类型的显式转换和隐式转换。

事实上在Rational r1=10已经运行了隐式转换，相应的转换代码例如以下：

 // Implicitly constructs and returns a Rational from an Int32 public static implicit operator Rational(Int32 num){return new Rational(num);}

假设将implicit换成explicit，Rational r1=10也将会报错(能够自行測试)。

转载请注明出处：http://blog.csdn.net/xxdddail/article/details/38057563