什么是用于设置对象属性的Linq表达式树？

Question

假设我有:

class Foo {
  public int Bar { get; set; }
}
public void SetThree( Foo x )
{
    Action<Foo, int> fnSet = (xx, val) => { xx.Bar = val; };
    fnSet(x, 3);
}

如何使用表达式树重写fnSet的定义,例如:

public void SetThree( Foo x )
{
   var assign = *** WHAT GOES HERE? ***
   Action<foo,int> fnSet = assign.Compile();

   fnSet(x, 3);
}

Answer 1

这是一个例子.

void Main()
{
   var fooParameter = Expression.Parameter(typeof(Foo));
   var valueParameter = Expression.Parameter(typeof(int));
   var propertyInfo = typeof(Foo).GetProperty("Bar");
   var assignment = Expression.Assign(Expression.MakeMemberAccess(fooParameter, propertyInfo), valueParameter);
   var assign = Expression.Lambda<Action<Foo, int>>(assignment, fooParameter, valueParameter);
   Action<Foo,int> fnSet = assign.Compile();

   var foo = new Foo();
   fnSet(foo, 3);
   foo.Bar.Dump();
}

class Foo {
    public int Bar { get; set; }
}

打印出"3".