作为主题,如何将两个表达式组合成一个表达式:
Expression<Func<IEnumerable<T>, IEnumerable<T>>> exp1;
Expression<Func<IEnumerable<T>, IEnumerable<T>>> exp2;
Expression<Func<IEnumerable<T>, IEnumerable<T>>> result = ???; // exp1(exp2)
答案 0 :(得分:8)
这实际上只是组合两个Expression<Func<T, T>>
值的特定形式。这是一个这样做的例子:
using System;
using System.Linq.Expressions;
public class Test
{
public static Expression<Func<T, T>> Apply<T>
(Expression<Func<T, T>> first, Expression<Func<T, T>> second)
{
ParameterExpression input = Expression.Parameter(typeof(T), "input");
Expression invokedSecond = Expression.Invoke(second,
new Expression[]{input});
Expression invokedFirst = Expression.Invoke(first,
new[]{invokedSecond});
return Expression.Lambda<Func<T, T>>(invokedFirst, new[]{input});
}
static void Main()
{
var addAndSquare = Apply<int>(x => x + 1,
x => x * x);
Console.WriteLine(addAndSquare.Compile()(5));
}
}
如果你想:
,你可以轻松地用这些术语写ApplySequence
public static Expression<Func<IEnumerable<T>, IEnumerable<T>>>
ApplySequence<T>
(Expression<Func<IEnumerable<T>, IEnumerable<T>>> first,
Expression<Func<IEnumerable<T>, IEnumerable<T>>> second)
{
return Apply(first, second);
}