c# Array Property based on other array

Question

I am looking to have an array property return the calculation of 2 other arrays at the same index (this has been answered using zip in another question Array property returns calculation of 2 other arrays). But now I have to set the value of the calculation.

public ushort[] LowLimit{ get; set; }

public ushort[] Range{ get; set; }

public ushort[] HiLimit => LowLimit.Zip(Range, (l,r) => (ushort)(l + r)).ToArray();

ie. if I set HiLimit[0], Range would be set to (value - LowLimit), how is this possible? Both getter and setter are required.

EDIT (2017-02-09): I have marked @dasblinkenlight answer as correct because its not possible. The reason I need this is because I am communicating with a device that sends a low limit and a range but the software allow the user to read and edit a low limit and high limit. The high and low limit are bound to controls on the display so I used properties for those and made two methods for setting and getting a range when communicating to the device.

public ushort[] LowLimit{ get; set; } = new ushort[8];

public ushort[] HighLimit{ get; set; } = new ushort[8];

public ushort getRange(int index) {
    ushort range = 0;

    if(index < 8)
        range = (ushort)(HighLimit[index] - LowLimit[index]);
    return range;
}

public void setRange(int index, ushort value) {
    if (index < 8)
        HighLimit[index] = (ushort)(LowLimit[index] + value);
}

FYI, The expression bodied property will perform the calculation/execute the code every time it is accessed. So each time you get a new array - it's not cached or stored in a field — pinkfloydx33
– pinkfloydx33, Commented Feb 6, 2017 at 15:15
LowLimit and Range come from the device that the software is communicating with. LowLimit and HiLimit are the parameters available to the user to edit in the software. — jsun5192
– jsun5192, Commented Feb 6, 2017 at 15:24

Sergey Kalinichenko · Accepted Answer · 2017-02-06 15:21:24Z

3

Making a computed property bi-directional is not possible, because computed properties are always read-only. Moreover, when you expose properties that return arrays, you have no control over modifications performed on the arrays that your methods return: arrays are inherently mutable, with no way to "watch" over changes to their elements.

You can solve this issue by providing a method for setting HiLimit, like this:

void SetHiLimit(int index, ushort newLimit) {
    // Change `Range` as needed
}

Note: You may reconsider the use of computed property for the array, because it is recomputed every time that you access it. For example, if you have HiLimit array of length 100, and you run a loop that accesses each element once, your code would recompute the array 100 times, creating 100 identical throw-away copies, with an overall asymptotic performance of O(n²).

edited Feb 6, 2017 at 15:21

answered Feb 6, 2017 at 15:15

Sergey Kalinichenko

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2 Comments

jsun5192 Over a year ago

I assume you mean making changes to computed array, if i wasnt using an array i could just add code to the getter and setter? The reason i was looking to use a property was for binding, the function will not work in this case.

Sergey Kalinichenko Over a year ago

@jsun5192 If you return a property of an array type, there would be no setter call when you do obj.HiLimit[1] = 123. You would see a call to the getter, but not the setter, because the assignment is performed on the array, not on the property.

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