C# Pass a property by reference

Question

Is there anyway to pass the property of an Object by reference? I know I can pass the whole object but I want to specify a property of the object to set and check it's type so I know how to parse. Should I maybe take another approach (I cannot change the original object in anyway)?

public class Foo{     public Foo(){}     public int Age { get; set; } }  private void setFromQueryString(object aProperty, String queryString, HttpContext context) {     //here I want to handle pulling the values out of      //the query string and parsing them or setting them     //to null or empty string...     String valueString = context.Request.QueryString[queryString].ToString();       //I need to check the type of the property that I am setting.      //this is null so I can't check it's type     Type t = aProperty.GetType(); }  private void callingMethod(HttpContext context) {     Foo myFoo = new Foo();     setFromQueryString(myFoo.Age, "inputAge", context); } 

Answer 1

You can call the function with a lambda expression:

private void setFromQueryString<T>(Action<T> setter, String queryString, HttpContext context)  {      //here I want to handle pulling the values out of       //the query string and parsing them or setting them      //to null or empty string...      String valueString = context.Request.QueryString[queryString].ToString();        //I need to check the type of the property that I am setting.       //this is null so I can't check it's type      Type t = typeof(T);      ...     setter(value); }  

You would call it like this:

setFromQueryString<int>(i => myFoo.Age = i, "inputAge", context); 

EDIT: If you really want type inference:

private void setFromQueryString<T>(Func<T> getter, Action<T> setter, String queryString, HttpContext context) {     ... } setFromQueryString(() => myFoo.Age, i => myFoo.Age = i, "inputAge", context); 

Answer 2

As others have pointed out, you can do this using delegates, using one of the many ways to specify delegates. However, if you intend to do this regularly, you should consider creating a wrapper type for passing properties by reference that wraps the delegates required, it may create a nicer API.

For example:

class PropertyReference<T> {    public T Value    {        get        {            return this.getter();        }         set        {            this.setter(value);        }    }     public PropertyReference(Func<T> getter, Action<T> setter)    {       this.getter = getter;       this.setter = setter;    } } 

That way you can pass around a reference to your property and modify it by setting the reference value.

var reference = new PropertyReference(                         () => this.MyValue,                         x => this.MyValue = x);  reference.Value = someNewValue;