C#, converting a case statement to a yield statement-CodePudding

I want to convert this statement to build a list of VM images to use in testing into something more elegant using the yield keyword, but the syntax is elluding me.

Desired end goal.

List<VmImages> images;
images[0] - WindowsServer2019
images[1] - WindowsServer2016
images[2] - RhelServer;
images[3] - OpenLogic;

Today the code looks like this:

            for (var i = 0; i < LinuxVMs; i  )
            {
                switch (i)
                {
                    case 0:
                        linuxDistros.Add(ConfigLoader.redHat);
                        break;
                    case 1:
                        linuxDistros.Add(ConfigLoader.openLogic);
                        break;
                    case 2:
                        linuxDistros.Add(ConfigLoader.suse);
                        break;
                    case 3:
                        linuxDistros.Add(ConfigLoader.ubuntu);
                        break;

                }

            }

This feels like a good case to use the yield keyword to simplify the logic into something like this, where I call GetLinuxVMs() for x number of times, where X is the count of LinuxVMs.

        private static IEnumerable<VmDistribution> GetLinuxVmDistros()
        {
            yield return ConfigLoader.redHat;
            yield return ConfigLoader.openLogic;
            yield return ConfigLoader.suse;
            yield return ConfigLoader.canonical;
        }

I'm not sure how to integrate this into my code, this is what I've tried:

            for (var i = 0; i < LinuxVMs; i  )
            {
                linuxDistros.Add(GetLinuxVmDistros());
            }

Since I get an IEnum back from the GetLinuxVmDistros method every time, I am puzzled as to how this is supposed to work at all.

CodePudding user response：

From your stated "desired end goal"

List<VmImages> images = new(){
    WindowsServer2019,
    WindowsServer2016,
    RhelServer,
    OpenLogic,
}

All the rest of the looping/finagling is just confusing the issue, IMHO

CodePudding user response：

GetLinuxVmDistros() will return an IEnumerable<VmDistribution> as per your definition.

It seems you want to add to a collection called linuxDistros another collection.

If linuxDistros is a List<VmDistribution>, simply use the AddRange method:

linuxDistros.AddRange(GetLinuxVmDistros());

See: https://docs.microsoft.com/fr-fr/dotnet/api/system.collections.generic.list-1.addrange?view=net-6.0

But I fail to see the point of creating an Enumerable just for this.

CodePudding user response：

I'm not certain what you try to achieve since the naming is .. not clear. But with this code below, it works:

class ConfigLoader
{
    static public VmDistribution redHat { get; set; } = VmDistribution.a;
    static public VmDistribution openLogic { get; set; } = VmDistribution.b;
    static public VmDistribution suse { get; set; } = VmDistribution.c;
    static public VmDistribution canonical { get; set; } = VmDistribution.d;
}

enum VmDistribution { a, b, c, d }
IEnumerable<VmDistribution> GetLinuxVmDistros()
{
    yield return ConfigLoader.redHat;
    yield return ConfigLoader.openLogic;
    yield return ConfigLoader.suse;
    yield return ConfigLoader.canonical;
}

var list = new List<VmDistribution>();
list.AddRange(GetLinuxVmDistros());

Notice that in the end I'm invoking GetLinuxVmDistros() only once, and the list is filled with method list.AddRange().

CodePudding user response：

In your example you should do whatever you need to do with the items with the loop.

for (var i = 0; i < LinuxVMs; i  )
{
    ProcessItem(LinuxVMs[i]);
}

Having said that, there's isn't much point in yielding on such a small set of results. The main purpose of yield return is to allow a large collection to be returned 1 item at a time, where the calling code may want to stop iterating over the items at any point. Another usage is where fetching all items at once may be very expensive resource-wise.

For example, you may not want to continue if 1 item couldn't be processed for whatever reason.

for (var i = 0; i < LinuxVMs; i  )
{
    var result = ProcessItem(LinuxVMs[i]);
    
    if (!result.Success)
    {
        break;
    }
}