Dictionary with a Point!!

Marty Habicht

Hi all,
I hope someone can help me out!! I'm fairly new to C#.

I've established a dictionary:
Dictionary<string, Point> addPositionDict = new Dictionary<string, Point>();

I initialized the dictionary:

Point addPoint = new Point();
addPoint.X = 0;
addPoint.Y = 0;

and added my points with their given names:

addPositionDict.Add(name_Out, addPoint);

Now knowing their names, I want to update their positions and I tried like so:

addPositionDict[nameOut].X = x_matrix;

However there is an error which I can't understand:
"Cannot modify the return value of 'System.Collections.Generic.Dictionary.this[string]' because it is not a variable"
What am I doing wrong? what exactly is not a variable? Again, Take it easy on the language "jargon" -- I'm fairly new to C#.

2 Replies

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Vulpes14y ago
Accepted answer
The problem is that Point is a struct (i.e. a value type) rather than a class.

Consequently, addPositionDict[name_Out].X is a value, rather than a variable, and you can't assign anything to a value.

The workaround is to do it like this:

addPositionDict[name_Out] = new Point(x_matrix, addPositionDict[name_Out].Y);

Notice that here addPositionDict[name_Out].Y is simply being used as a value - we're not trying to assign anything to it.

If Point had been a class (i.e. a reference type) rather than a struct, then your original code would have worked because addPositionDict[name_Out].X would then have been regarded as a variable.
Marty Habicht14y ago
Tahak you so much for this! For once nobody is speaking in "#" jargon. Easy to understand. Wow!!