替换它
我有一个方法方法
private static int Method(int n)
{
return n;
}
我在我的表达式视图中的" vistmethodcall"中获得了MethodCallexPression。MethodCallexPression包含:
n => Method(2 + n)
我想将其编译为func并这样打电话:
func(3)
应该返回5。
我尝试了:
IEnumerable<ParameterExpression> parameters = expression.Arguments.Select(a => Expression.Parameter(a.Type, a.ToString()));
MethodCallExpression call = Expression.Call(expression.Method, parameters);
Expression<Func<Int32, Int32>> lambda = Expression.Lambda<Func<int, int>>(call, call.Arguments.OfType<ParameterExpression>());
var func = lambda.Compile();
Console.WriteLine(func(3));
它是返回我3,而不是5
这是因为2 x是param名称,我用3。
不确定为什么要这样做,但是无论如何要这样做,您需要提取 MethodCallExpression
使用的参数(不是参数)。为此,您可以这样滥用表达访问者:
public class ParametersExtractorVisitor : ExpressionVisitor {
public IList<ParameterExpression> ExtractedParameters { get; } = new List<ParameterExpression>();
protected override Expression VisitParameter(ParameterExpression node) {
ExtractedParameters.Add(node);
return base.VisitParameter(node);
}
}
然后在您的代码中使用它:
var visitor = new ParametersExtractorVisitor();
visitor.Visit(expression);
MethodCallExpression call = Expression.Call(expression.Method, expression.Arguments);
Expression<Func<Int32, Int32>> lambda = Expression.Lambda<Func<int, int>>(call, visitor.ExtractedParameters);
var func = lambda.Compile();
Console.WriteLine(func(3));
您不需要访问者就可以实现它。
基本上,应在将值传递给lambda的情况下以2。
Method
函数。
using System;
using System.Linq.Expressions;
using System.Reflection;
namespace Test
{
class Program
{
static void Main(string[] args) {
var method = typeof(Program).GetMethod("Method", BindingFlags.Static | BindingFlags.Public);
var parameter = Expression.Parameter(typeof(int), "n");
var add = Expression.Add(Expression.Constant(2, typeof(int)), parameter);
var methodCallExpression = Expression.Call(null, method, add);
var lambda = Expression.Lambda<Func<int, int>>(methodCallExpression, parameter);
var func = lambda.Compile();
Console.WriteLine(func(3));
}
public static int Method(int n) => n;
}
}
我将通过访客突变
来实现它using System;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
namespace Test
{
class MethodCallVisitor : ExpressionVisitor
{
private readonly int toAdd;
public MethodCallVisitor(int toAdd) {
this.toAdd = toAdd;
}
protected override Expression VisitMethodCall(MethodCallExpression node) {
var add = Expression.Add(node.Arguments.First(), Expression.Constant(toAdd));
return Expression.Call(node.Object, node.Method, add);
}
}
class Program
{
static void Main(string[] args) {
var methodCallVisitor = new MethodCallVisitor(2);
var method = typeof(Program).GetMethod("Method", BindingFlags.Static | BindingFlags.Public);
var parameter = Expression.Parameter(typeof(int), "n");
var methodCallExpression = Expression.Call(null, method, parameter);
var lambda = Expression.Lambda<Func<int, int>>(methodCallExpression, parameter);
lambda = (Expression<Func<int, int>>)methodCallVisitor.Visit(lambda);
var func = lambda.Compile();
Console.WriteLine(func(3));
}
public static int Method(int n) => n;
}
}