CODEWITHSUNDEEP
c#propertiesargumentsparameter-passing
Xantham
Xantham

Reputation: 1899

Passing a pointer to a class property

Edit: This is an example program, I understand that there is a sum operator in linq. However, I was trying to ask specifically on how to pass the pointer to the property to do something complex with it, not necessarily this summing algorithm.

Lets say I have a class like this:

class Point
{
    double x {get; set;}
    double y {get; set;}
}

and in my main program I had 2 functions.

double function1(List<Point> PointList)
{
   double sum = 0.0;
   foreach(Point p in PointList)
   {
      sum += p.x;
   }       
   return sum;
}

double function2(List<Point> PointList)
{
   double sum = 0.0;
   foreach(Point p in PointList)
   {
      sum += p.y;
   }       
   return sum;
}

These functions are completely identical except one is summing the X values, the other is summing the Y values. Since these are so similar, I would like to combine them such that I basically pass in that List of Points, and something to identify that I want to do the X or the Y based calculation.

I know I could put in a switch statement and tell it whether it was the X or the Y based on an enum, or a number that is defined to tell it to do the X or the Y. If this was a normal function, I suppose I could use s delegate, but this is a property, so I'm not sure how that translates.

So how do I combine those functions into something like:

double bothFunctions(List<Point> PointList, var propertyToUse)
{
   double sum = 0.0;
   foreach(Point p in PointList)
   {
      sum += p.propertyToUse;
   }       
   return sum;
}

Where propertyToUse points to either X or Y.

Upvotes: 3

Views: 3594

Answers (3)

Oscar Mederos
Oscar Mederos

Reputation: 29813

The current solutions work great, but they assume either that your operation is sum, or that you will have only two possible properties (X and Y).

If you want more freedom, you can do:

double function(List<Point> PointList, Func<Point, double> selector)
{
    double sum = 0.0;
    foreach (Point p in PointList)
    {
        sum += selector(p);
    }
    return sum;
}

Then you call it like this:

double sumX = function(PointList, p => p.X);
double sumY = function(PointList, p => p.Y);

you'll be able to write more complicated selectors, like:

double sumXY = function(PointList, p => p.X + p.Y);

Upvotes: 7

JG in SD
JG in SD

Reputation: 5607

You should look at using the Enumerable.Sum extension method instead of writing your own.

var sumX = pointList.Sum(item => item.X);
var sumY = pointList.Sum(item => item.Y);

You will need to add using System.Linq; if not already present in your code file.

Upvotes: 2

Yuck
Yuck

Reputation: 50835

I think you're making it too complicated. You can use a method like this:

double bothFunctions(List<Point> PointList, bool sumX)
{
   double sum = 0.0;
   foreach(Point p in PointList)
   {
      if (sumX)
          sum += p.x;
      else
          sum += p.y;
   }       
   return sum;
}

Or just use LINQ:

var ySum = pointList.Sum(e => e.y);
var xSum = pointList.Sum(e => e.x);

Upvotes: 0

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