使用命名参数常量调用 MethodCallExpression

Question

假设我有这样的功能

public string TestValue(string hello, Guid world)
{
    return hello + world;
}

假设objectParams 是对象Dictionary<string, object> 的字典，将参数名称映射到值，我目前正在将参数值与方法名称匹配，如下所示：

var method = this.GetType().GetMethod("TestValue");
var methodParameters = method.GetParameters();
var paramMatcher = (from paramValue in objectParams
                    from methodParam in methodParameters
                    where param.Key == clrParam.Name
                    select (name: clrParam.Name,
                            type: clrParam.ParameterType,
                            value: paramValue.Value));

然后我构建表达式来调用方法TestValue，就像这样，但这是我遇到问题的部分。

var paramExpress = (from param in paramMatcher
                    select Expression.Assign(Expression.Parameter(param.type, param.name), Expression.Constant(param.value)));

Func<object> result = Expression.Lambda<Func<object>(Expression.Call(Expression.Constant(this),
    method, paramExpress)).Compile();
var res = result.Invoke(); //should return 'somestringxxxxxxx-xxxx...etc'

问题是我不能保证参数值是按调用顺序的，所以我想依靠参数的名称来调用。我不确定如何正确地将常量值分配给它们的参数表达式。运行此代码会导致编译 lambda 时出现异常 System.InvalidOperationException: 'variable 'hello' of type 'System.String' referenced from scope '', but it is not defined'。

Answer 1

Expression.Assign是一个二元运算，所以左边的变量取了一个表达式右边计算的新值。

在这些方面：

var paramExpress = (from param in paramMatcher
     select Expression.Assign(Expression.Parameter(param.type, param.name),
                Expression.Constant(param.value, param.type)));

Func<object> result = Expression.Lambda<Func<object>(Expression.Call(Expression.Constant(this),
    method, paramExpress)).Compile();

您已收到但未使用实际参数值，显示在二进制表达式的右侧部分中。

解决方案：

public class C
{
    public string TestValue(string hello, Guid world)
    {
        return hello + world;
    }

    public string Execute()
    {
        var objectParams = new Dictionary<string, object>()
        {
            {"hello", "somestring"},
            {"world", Guid.NewGuid()}
        };
        var method = this.GetType().GetMethod("TestValue");
        var methodParameters = method.GetParameters();
        var paramMatcher = (from paramValue in objectParams
            from methodParam in methodParameters
            where paramValue.Key == methodParam.Name
            orderby methodParam.Position  // <-- preserves original order
            select (name: methodParam.Name,
            type: methodParam.ParameterType,
            value: paramValue.Value));

        var paramExpress = (from param in paramMatcher
             select Expression.Assign(Expression.Parameter(param.type, param.name),
                    Expression.Constant(param.value, param.type)));

        var values = paramExpress.Select(v => v.Right); // !!!

        Func<string> result = Expression.Lambda<Func<string>>(Expression.Call(Expression.Constant(this),
            method, values)).Compile();
        return result.Invoke(); // returns "somestringxxxxxxx-xxxx..."
    }
}