构建一个检查对象的两个属性是否相等的表达式？

Question

我试图了解 Expressions 是如何工作的，所以我设想了一个方法，该方法采用一个具有两个 int 属性和 return 布尔值的对象来指示它们是否相等，类似于：

bool AreEqual(Foo foo)
{
    return foo.Value1 == foo.Value2;
}

这是我构建的表达式：

//build the parameter expression of the object
ParameterExpression parameter = Expression.Parameter(typeof(Foo), "x");
//the left member
MemberExpression leftMember = Expression.Property(parameter, "Value1");
//the right member
MemberExpression rightMember = Expression.Property(parameter, "Value2");
//the left lambda
LambdaExpression leftLmbda = Expression.Lambda(leftMember, parameter);
//the right lambda
LambdaExpression rightLambda = Expression.Lambda(rightMember, parameter);
//and here I evaluate the boolean expression:
Expression equalExpression = Expression.Equal(rightLambda, leftLmbda);
//the lambda of the equal expression
LambdaExpression lambda = Expression.Lambda(equalExpression, parameter);

//the object:
Foo foo = new Foo { Value1= 5, Value2=5 };

Delegate expression = lambda.Compile();
var eq = expression.DynamicInvoke(foo);

但它的计算结果总是 false。

我的猜测是我只构建了一个 lambda，但不知道如何在一个 lambda 中处理两个属性

Answer 1

您的 Expression.Equal 语句应该比较两个成员表达式。

//build the parameter expression of the object
ParameterExpression parameter = Expression.Parameter(typeof(Foo), "x");
//the left member
MemberExpression leftMember = Expression.Property(parameter, "Value1");
//the right member
MemberExpression rightMember = Expression.Property(parameter, "Value2");
//and here I evaluate the boolean expression:
Expression equalExpression = Expression.Equal(leftMember, rightMember);
//the lambda of the equal expression
LambdaExpression lambda = Expression.Lambda(equalExpression, parameter);

//the object:
Foo foo = new Foo { Value1 = 5, Value2 = 5 };

Delegate expression = lambda.Compile();
var eq = expression.DynamicInvoke(foo);

构建一个检查对象的两个属性是否相等的表达式？

Building an Expression that checks if two properties of the object are equal?

c#

lambda

expression-trees