LambdaExpression变量引用从范围但没有定义 [英] LambdaExpression Variable Referenced From Scope But Not Defined

问题描述

我有一个简单的lambda表达式，我想编译并调用

I have a simple lambda expression that I would like to compile and invoke

Expression< Func< Commands, bool>> expression = c => c.IsValid("test");

但是当我做了以下内容：

but when I do the following:

LambdaExpression le = Expression.Lambda(expression.Body);

object result = le.Compile().DynamicInvoke();

编译引发错误：

the compile throws the error:

型的'ConsoleApplication1.Commands距离范围'引用，但它没有定义

variable 'c' of type 'ConsoleApplication1.Commands' referenced from scope '', but it is not defined

如何设置，该表达式的实例变量？

How do you set the instance variable for this expression?

推荐答案

为什么不直接编译表达式本身呢？如果您想与一些特定的ConsoleApplication1.Commands实例来调用它多次，然后你可以正好接近了该实例：

Why not just compile the expression itself? If you'd like to invoke it with some specific 'ConsoleApplication1.Commands' instance multiple times you could then just close over that instance:

var validator = expression.Compile();

var c = new Commands();
var validatorForC = () => validator(c);

否则，你就需要建立呼叫的表情，像这样的：

Otherwise you'll need to build call expression, like this:

var c = new Commands();
var le = Expression.Lambda(Expression.Invoke(expression, Expression.Constant(c)));
object result = le.Compile().DynamicInvoke();

也可以使ExpressionVisitor将取代C参数的所有出现在expression.Body与Expression.Constant。

or you can make ExpressionVisitor which will replace all occurences of the 'c' parameter in 'expression.Body' with Expression.Constant.

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