本教程展示如何定義轉換以及如何在類或結構之間使用轉換。
請參見“用戶定義的轉換”示例以下載和生成本教程中討論的示例文件。
C# 允許程序員在類或結構上聲明轉換，以便可以使類或結構與其他類或結構或者基本類型相互進行轉換。轉換的定義方法類似於運算符，並根據它們所轉換到的類型命名。
在 C# 中，可以將轉換聲明為 implicit（需要時自動轉換）或 explicit（需要調用轉換）。所有轉換都必須為 static，並且必須采用在其上定義轉換的類型，或返回該類型。
本教程介紹兩個示例。第一個示例展示如何聲明和使用轉換，第二個示例演示結構之間的轉換。
本示例中聲明了一個 RomanNumeral 類型，並定義了與該類型之間的若干轉換。
// conversion.cs
using System;
struct RomanNumeral
{
public RomanNumeral(int value)
{
this.value = value;
}
// Declare a conversion from an int to a RomanNumeral. Note the
// the use of the operator keyword. This is a conversion
// operator named RomanNumeral:
static public implicit operator RomanNumeral(int value)
{
// Note that because RomanNumeral is declared as a struct,
// calling new on the struct merely calls the constructor
// rather than allocating an object on the heap:
return new RomanNumeral(value);
}
// Declare an explicit conversion from a RomanNumeral to an int:
static public explicit operator int(RomanNumeral roman)
{
return roman.value;
}
// Declare an implicit conversion from a RomanNumeral to
// a string:
static public implicit operator string(RomanNumeral roman)
{
return("Conversion not yet implemented");
}
private int value;
}
class Test
{
static public void Main()
{
RomanNumeral numeral;
numeral = 10;
// Call the explicit conversion from numeral to int. Because it is
// an explicit conversion, a cast must be used:
Console.WriteLine((int)numeral);
// Call the implicit conversion to string. Because there is no
// cast, the implicit conversion to string is the only
// conversion that is considered:
Console.WriteLine(numeral);
// Call the explicit conversion from numeral to int and
// then the explicit conversion from int to short:
short s = (short)numeral;
Console.WriteLine(s);
}
}
10 Conversion not yet implemented 10
本示例定義 RomanNumeral 和 BinaryNumeral 兩個結構，並演示二者之間的轉換。
// structconversion.cs
using System;
struct RomanNumeral
{
public RomanNumeral(int value)
{
this.value = value;
}
static public implicit operator RomanNumeral(int value)
{
return new RomanNumeral(value);
}
static public implicit operator RomanNumeral(BinaryNumeral binary)
{
return new RomanNumeral((int)binary);
}
static public explicit operator int(RomanNumeral roman)
{
return roman.value;
}
static public implicit operator string(RomanNumeral roman)
{
return("Conversion not yet implemented");
}
private int value;
}
struct BinaryNumeral
{
public BinaryNumeral(int value)
{
this.value = value;
}
static public implicit operator BinaryNumeral(int value)
{
return new BinaryNumeral(value);
}
static public implicit operator string(BinaryNumeral binary)
{
return("Conversion not yet implemented");
}
static public explicit [1] [2] 下一頁
operator int(BinaryNumeral binary)
{
return(binary.value);
}
private int value;
}
class Test
{
static public void Main()
{
RomanNumeral roman;
roman = 10;
BinaryNumeral binary;
// Perform a conversion from a RomanNumeral to a
// BinaryNumeral:
binary = (BinaryNumeral)(int)roman;
// Performs a conversion from a BinaryNumeral to a RomanNumeral.
// No cast is required:
roman = binary;
Console.WriteLine((int)binary);
Console.WriteLine(binary);
}
}
10 Conversion not yet implemented
binary = (BinaryNumeral)(int)roman;
執行從 RomanNumeral 到 BinaryNumeral 的轉換。由於沒有從 RomanNumeral 到 BinaryNumeral 的直接轉換，所以使用一個轉換將 RomanNumeral 轉換為 int，並使用另一個轉換將 int 轉換為 BinaryNumeral。
roman = binary;
執行從 BinaryNumeral 到 RomanNumeral 的轉換。由於 RomanNumeral 定義了從 BinaryNumeral 的隱式轉換，所以不需要轉換。
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