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I'm parsing a JSON string using MiniJson in Unity. Now I have a value that's a list of strings. Though I get this an object. The underlying type of the object is a List<object>, but actually it should be a List<string>. So currently I do this:

void SetInfo(Dictionary<string,object> info) {
    Colors = (info["colors"] as List<object>).OfType<string>().ToList();
}

The dictionary is what I get from the MiniJson library. This works perfectly. Though seems a bit ugly, a lot of unnecessary casting, and I was wondering if there's a better way of doing this. Mostly I'm looking for cleaner code, and faster execution, since there are a lot of these entries.

Edit: I wasn't very clear about this. In the info dictionary there are a bunch of key/value pairs, the type of the values vary. I can cast most very easily, but the info["colors"] object is the one I'm having problems with.

So when I do info["colors"] I get an object, with an underlying type List<object>. The objects in this list are actually strings.

Also, there's not really a performance problem here, since it's only called once at the start of the program, though there is a noticeable lag currently, I'm going to put it on it's own thread anyway so no problem there. The faster execution is just out of curiosity.

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  • did you measure the performance and confirmed that there is a performance problem? Commented Apr 16, 2014 at 9:29
  • 3
    "The underlying type of the object is a List, but actually it should be a List" you mean dictionary? Commented Apr 16, 2014 at 9:29
  • Why is it not sent in as Dictionary<string, List<string>>? Commented Apr 16, 2014 at 9:31
  • @Weyland, I mean the underlying type of the object I get when I do info["colors"]. @Magnus, there are other values in it aswell. For instance the info["cmc"] is an int. Commented Apr 16, 2014 at 9:34
  • I edited my question. I'm only just awake, and my question suffered for it. Should be more clear now I hope. Commented Apr 16, 2014 at 9:39

3 Answers 3

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Try this one.

(info["colors"] as List<object>).ConvertAll(input => input.ToString());

you can also use direct cast (string)input or input as string which is even faster(there were debates on casting here at stackoverflow).

info["colors"] as List<object> can result in null, so I'd rather be more safe and wrap your code like this:

List<object> colors = info["colors"] as List<object>;
List<string> typedColors = null;
if (colors!=null)
{
   typedColors = colors.ConvertAll(input => input as string);
}
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3 Comments

This is a good solution. Though almost the same. Is there a reason why ConvertAll is preferred over my .OfType<string>().ToList(); Other than being only one call?
OfType is an extension method and is not a conversion method, it only returns elements that are already of the specified type, and it will be of type IEnumerable<T>. Meanwhile ConvertAll is not an extension method - it's native method of List class. You don't have to convert IEnumerable to List and you can convert every element like you need.
I think you can also use colors.Cast<string>() safely if you are sure about all items been of type string.
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Have you thought about using the in and out keywords

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3 Comments

For this problem not, what do you propose?
Lists(as they are classes) cannot be variant. You can define custom contravariant interface ICustomList<in T> to make something like ICustomList<string> = ICustomList<object>. But why should you do that, it will cast implicitly anyways.
ah, I think I have misunderstood how the in and out keywords work then. I have never used them but came across the pages I linked to in my comment and thought they might be helpful. Ah well, sorry!
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I know this code is a bit old school, but we all know what it means:

    List<object> l = new List<object>();
    List<string> s = new List<string>();
    foreach( var i in l )
        s.Add((string)i);
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