构造函数不能接受输入类型表达式<Func<T, TResult> &gt; 在 C# 中

Question

I want to create the class Foo as follows.

The Foo constructor input expression has to get some member of Type T to do some work.

class Foo<T>
{
    public Foo<TResult>(Expression<Func<T, TResult>> selector)
    {
         List<string> memberNames = typeof(TR).GetProperties().Select(p => p.Name).ToList();
         ....//some work on memberNames 
    }
}

and create Foo<T> instance by this code:

Foo<ClassA> foo = new Foo<ClassA>(u=>new{u.Property1, u.Property2});

However, this did not work and gave the following error:

Constructor can't have Generic type TResult.

How can I fix this?

Edit:

After struggling to understand the expression I found an answer and have written it as an answer.

Answer 1

You can move the logic outside of consrtuctor to separate method. Instead of using constructor to create Foo - you can use static method, like this:

class Foo<T> {
    private Foo() {

    }

    private void Init<TResult>(Expression<Func<T, TResult>> selector) {
        List<string> memberNames = typeof(TResult).GetProperties().Select(p => p.Name).ToList();
        //some work on memberNames 
    }

    public static Foo<T> Create<TResult>(Expression<Func<T, TResult>> selector) {
        var foo = new Foo<T>();
        foo.Init(selector);
        return foo;
    }
}

And use it like this:

Foo<ClassA> foo = Foo<ClassA>.Create(u=>new{u.Property1, u.Property2});

Answer 2

I solve that as follow

class ClassA
{
    public int MyProperty { get; set; }
    public int MyProperty2 { get; set; }
}    
class Foo<T>
{
    public Foo(Expression<Func<T, Object>> selector)
    {
        var props = ((NewExpression)selector.Body).Members.Select(p => p.Name).ToList();
    }
}

Foo<ClassA> foo = new Foo<ClassA>(u => new { u.MyProperty, u.MyProperty2 });