转换表达式来; Func键< T，T2，布尔>>到表达式来; Func键< T2，布尔>>通过引入一个常数对于T [英] Convert Expression<Func<T, T2, bool>> to Expression<Func<T2, bool>> by introducing a constant for T

问题描述

我在表达式来的格式表达; Func键< T，T2，布尔>> ，我需要转换为表达对格式表达式来; Func键< T2，布尔>>

I have an expression in the format of Expression<Func<T, T2, bool>> that I need to convert into an expression on the format of Expression<Func<T2, bool>> by replacing the T in the first expression with a constant value.

我这需要留下来作为一种表达，所以我不能只调用一个常量作为第一个参数的表达。

I need this to stay as an expression so I can't just Invoke the expression with a constant as the first parameter.

我在其他问题看这里表达左右树木，我真的不能找到解决我的问题。我怀疑我必须走表达式树介绍常数和删除一个参数，但我甚至不知道此刻开始。 （

I've looked at the other questions here about expression trees but I can't really find a solution to my problem. I suspect I have to walk the expression tree to introduce the constant and remove one parameter but I don't even know where to start at the moment. :(

推荐答案

您可以使用的 Expression.Invoke 来创建调用其他新的lambda表达式：

You can use Expression.Invoke to create a new lambda expression that calls the other:

static Expression<Func<T2, bool>> PartialApply<T, T2>(Expression<Func<T, T2, bool>> expr, T c)
{
    var param = Expression.Parameter(typeof(T2), null);
    return Expression.Lambda<Func<T2, bool>>(
        Expression.Invoke(expr, Expression.Constant(c), param), 
        param);
}

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