Value type property and C# compilation error

Two days ago a question was asked in StackOverflow.com and I found this question so good to prepare a post. I want to explain this question:

Petr asked: I do not understand why there is Control.padding.all which is int and according to hint there is set as well as get but I cannot set it (Control.Padding.All=5)? I would be grateful for explanation.

For example when you want to set

	textBox1.Padding.All = 5;

You will get this compiling error: Cannot modify the return value of 'System.Windows.Forms.TextBoxBase.Padding' because it is not a variable

Following example is an implementation of this error:

    public class ARAControl 
    { 
        public ARAPadding Padding { get; set; } 
    }
    public struct ARAPadding 
    { 
        public int All { get; set; } 
    }

If you use this you'll get mentioned error:

	ARAControl control = new ARAControl(); 
	control.Padding.All = 10;

And why this compiling error happens. It hapens because structure is a value type. By setting this property you first call get Method. "Property Get" will return a copy of ARAPadding, so it is a value type and C# will detect out mistake and prevent compiling.