c# - 投然后检查还是检查然后投？

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Possible Duplicate:
Casting vs using the ‘as’ keyword in the CLR

哪种方法被认为是最佳实践？

先投？

public string Describe(ICola cola)
{
    var coke = cola as CocaCola;
    if (coke != null)
    {
        string result;
        // some unique coca-cola only code here.
        return result;
    }
    var pepsi = cola as Pepsi;
    if (pepsi != null)
    {
        string result;
        // some unique pepsi only code here.
        return result;
    }
}

还是先check，再cast？

public string Describe(ICola cola)
{
    if (cola is CocaCola)
    {
        var coke = (CocaCola) cola;
        string result;
        // some unique coca-cola only code here.
        return result;
    }
    if (cola is Pepsi)
    {
        var pepsi = (Pepsi) cola;
        string result;
        // some unique pepsi only code here.
        return result;
    }
}

你能找到其他方法吗？

最佳答案

如果对象可能是也可能不是您想要的类型，那么 as 运算符(您的第一种方法)在两个方面更好: