如何创建，要么抛出一个异常或返回基于条件值的表达式？ [英] How can I create an expression that either throws an exception or returns a value based on a condition?

问题描述

我挣扎建立，如果条件为真抛出异常表达，如果它是假的，它应该返回一个值，但我总是得到的ArgumentException ：

I'm struggling to build an expression that if the condition is true throws an exception and if it's false that it should return a value but I'm always getting the ArgumentException:

var expr =
    Expression.Condition(
        Expression.Equal(Expression.Constant(0), Expression.Constant(0)),
        Expression.Throw(Expression.Constant(new DivideByZeroException())),
        Expression.Constant(1));
var lambda = Expression.Lambda<Func<int>>(expr);
var result = lambda.Compile()();

如果我把 Expression.Empty（）作为条件的第三个参数它然后运行，但如果条件是假的我没有得到期望的结果。

If I put Expression.Empty() as the third argument of the Condition it then runs but I don't get the desired result if the condition is false.

推荐答案

该做的。

var expr =
    Expression.Block(
        Expression.IfThen(
            Expression.Equal(Expression.Constant(1), Expression.Constant(1)),
            Expression.Throw(
                Expression.New(typeof(DivideByZeroException))
            )
        ),
        Expression.Constant(1)
    );
var lambda = Expression.Lambda<Func<int>>(expr);
var result = lambda.Compile()();

条件更类似于三元运算符。所以，你在写什么在C＃更加等价于：

Conditional is more similar to the ternary operator. So what you were writing was more equivalent to in C#:

return (0 == 0) ? throw new DivideByZeroException() : 1;

我改变了你的不变异常动态创建的，我假设是首选。

I changed your constant exception to a dynamically created one, I'm assuming that is preferred.

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