Prefer the is or as Operators to Casts - Effective C#学习笔记(3)
2008-03-16 14:56
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这里的Casts精确来说应该是DownCasts ,因为向上转型是不用强制类型转换的。
如果我们要把一个object型的变量转换为自己的类型(类类型)MyType,用DownCast的做法是
object o = Factory.GetObject();
MyType mt = (MyType) o;
以上的代码是有漏洞的,
完美的防御性的代码应该这么写:
object o = Factory.GetObject();
MyType mt;
try {
mt = (MyType) o;
} catch (Exception e) {
//Report the failure
}
if(mt != null) {
//Work with mt
} else {
//Report the failure
}
现在可以看到DownCast的代码是多么丑陋了,换作as运算符,则会很优雅:
object o = Factory.GetObject();
MyType mt = o as MyType;
if(MyType != null) {
//Work with mt
} else {
//Report the failure
}
应当注意的是as运算符适用于类类型而非值类型
在值类型中运用强制转换有时候会丢失精度,比如如果把一个long型转换为int型,这样是可以转换的,但会丢失精度,由64位变为32位,而有时候我们并不希望这么做,这时候可以用is运算符:
object o = Factory.GetValue( );
int i = 0;
if ( o is int ) {
i = ( int ) o;
}
如果我们要把一个object型的变量转换为自己的类型(类类型)MyType,用DownCast的做法是
object o = Factory.GetObject();
MyType mt = (MyType) o;
以上的代码是有漏洞的,
完美的防御性的代码应该这么写:
object o = Factory.GetObject();
MyType mt;
try {
mt = (MyType) o;
} catch (Exception e) {
//Report the failure
}
if(mt != null) {
//Work with mt
} else {
//Report the failure
}
现在可以看到DownCast的代码是多么丑陋了,换作as运算符,则会很优雅:
object o = Factory.GetObject();
MyType mt = o as MyType;
if(MyType != null) {
//Work with mt
} else {
//Report the failure
}
应当注意的是as运算符适用于类类型而非值类型
在值类型中运用强制转换有时候会丢失精度,比如如果把一个long型转换为int型,这样是可以转换的,但会丢失精度,由64位变为32位,而有时候我们并不希望这么做,这时候可以用is运算符:
object o = Factory.GetValue( );
int i = 0;
if ( o is int ) {
i = ( int ) o;
}
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