Multiple return values into object properties

Question

I have read the article about multiple returns a number of times. But I cannot figure out how to apply it when the values that I am trying to get out are not be destructed into simple scalars, but rather object properties. (I can use C# V7 if needed).

Also the out keyword is not allowed when with parameters that are object properties. So how can I do this example:

Tools.orientation(ent.esr, out e.heading, out e.pitch, out e.roll);

//...

public static void orientation(EntityStateRepository esr, out double  heading, out double pitch, out double roll)
{
    TaitBryan topoEuler = topoToGeoc.eulerTrans(esr.worldOrienation);
    heading = MathHelper.RadiansToDegrees(topoEuler.psi);
    pitch = MathHelper.RadiansToDegrees(topoEuler.theta);
    roll = MathHelper.RadiansToDegrees(topoEuler.phi);
}

I think you are over thinking this. Define a new type with those properties and return an instance of that type. — Igor, Oct 03 '17 at 20:12
The function is only filling in a few of those values, should I just pass in the object and let it do the rest? — Dr.YSG, Oct 03 '17 at 20:13
@Dr.YSG the parameter should be the object, the return value should be the object. Modify it in the method, then return the modified object. — maccettura, Oct 03 '17 at 20:15
What about [`ValueTuples`](https://blogs.msdn.microsoft.com/mazhou/2017/05/26/c-7-series-part-1-value-tuples/) in C# 7? — Salah Akbari, Oct 03 '17 at 20:21
I was using ValueTuples, but it looked a little verbose for me to first deconstruct the Tuple, and then stuff it into the Entry.e object. I think I am going with @maccettura approach, which I just compiled and ran. — Dr.YSG, Oct 03 '17 at 20:27

Igor · Answer 1 · 2017-10-03T20:18:07.853

3

I think you are over thinking this. Define a new type with those properties and return an instance of that type. For example:

public static OrientationModel orientation(EntityStateRepository esr)
{
    TaitBryan topoEuler = topoToGeoc.eulerTrans(esr.worldOrienation);
    var container = new OrientationModel();

    container.heading = MathHelper.RadiansToDegrees(topoEuler.psi);
    container.pitch = MathHelper.RadiansToDegrees(topoEuler.theta);
    container.roll = MathHelper.RadiansToDegrees(topoEuler.phi);

    return container;
}

public sealed class OrientationModel {
    public decimal heading {get;set;}
    public decimal pitch {get;set;}
    public decimal roll {get;set;}
}

edited Oct 03 '17 at 20:18

answered Oct 03 '17 at 20:14

Igor

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@xxbbcc - True, it was meant as an example but maybe this is more clear. – Igor Oct 03 '17 at 20:16
@Igor why use `ref` parameters at all? The OP is trying to pass properties by reference - why not just pass the object in instead of the properties? – D Stanley Oct 03 '17 at 20:17
@DStanley - because I got sloppy with my copy/paste and read past it. More on your point though they are not used at all so they could just be omitted. – Igor Oct 03 '17 at 20:18
@DStanley I think Igor just forgot to change the parameters from the OP code – maccettura Oct 03 '17 at 20:19

score 2 · Accepted Answer · answered Oct 03 '17 at 20:17

You can't pass properties by reference, so your best bet is to pass in the parent object instead:

Tools.orientation(ent.esr, e);

//...

public static void orientation(EntityStateRepository esr, TypeOfE e)
{
    TaitBryan topoEuler = topoToGeoc.eulerTrans(esr.worldOrienation);
    e.heading = MathHelper.RadiansToDegrees(topoEuler.psi);
    e.pitch = MathHelper.RadiansToDegrees(topoEuler.theta);
    e.roll = MathHelper.RadiansToDegrees(topoEuler.phi);
}

Or if you want to keep the version with out parameters and add an overload instead:

public static void orientation(EntityStateRepository esr, TypeOfE e)
{
    double heading;
    double pitch;
    double roll;
    Tools.orientation(ent.esr, out heading, out pitch, out roll);
    e.heading = heading;
    e.pitch = pitch;
    e.roll = roll;
}
//...

public static void orientation(EntityStateRepository esr, out double  heading, out double pitch, out double roll)
{
    TaitBryan topoEuler = topoToGeoc.eulerTrans(esr.worldOrienation);
    heading = MathHelper.RadiansToDegrees(topoEuler.psi);
    pitch = MathHelper.RadiansToDegrees(topoEuler.theta);
    roll = MathHelper.RadiansToDegrees(topoEuler.phi);
}

score 2 · Answer 3 · answered Oct 03 '17 at 20:31

Just for completeness sake, you mentioned multiple return types.

With C# 7 features, and the NuGet Package System.ValueTuple you could write the following, and it would be equivalent to Igor's answer unless you are going to re-use the SomeContainer class

public static (double heading, double pitch, double roll) orientation(EntityStateRepository esr)
{
    TaitBryan topoEuler = topoToGeoc.eulerTrans(esr.worldOrienation);

    var h = MathHelper.RadiansToDegrees(topoEuler.psi);
    var p = MathHelper.RadiansToDegrees(topoEuler.theta);
    var r = MathHelper.RadiansToDegrees(topoEuler.phi);

    return (h, p, r);
}

And access with

var res = orientation(...);
DoAThing(res.heading);
DoAThing(res.pitch);
DoAThing(res.roll);

Multiple return values into object properties

3 Answers3