Dictionary extension compiles but not callable

Question

I am doing the exact same thing as mentioned here:Which mechanism is a better way to extend Dictionary to deal with missing keys and why?

Making a getter to a dictionary that returns a default. It compiles just fine but anyone trying to use it gets a compiler error saying … and no extension method 'ObjectForKey' accepting a first argument of type System.collections.Genericc.Dictionary could be found.

Here is the definition

public static TValue ObjectForKey<TKey,TValue>(this Dictionary<TKey,TValue> dictionary, TKey key)
{
    TValue val = default(TValue);
    dictionary.TryGetValue(key,out val);
    return val;
}

Here is how I try to use it

Dictionary<string,object> dictionary = <stuff>
object val = dictionary.ObjectForKey("some string");

Any thoughts?

I'm not getting this error here. Please provide more context, or try reducing the use case to its minimum, maybe as a new project. — Luc Morin, Feb 11 '14 at 04:21

Selman Genç · Accepted Answer · 2014-02-11T20:00:25.963

2

You should define your extension method inside of a static (to make is extension) and public (to make it accessible outside of the class) class

public static class MyExtensions
{
    public static TValue ObjectForKey<TKey,TValue>(this Dictionary<TKey,TValue> dictionary, TKey key)
    {
        TValue val = default(TValue);
        dictionary.TryGetValue(key,out val);
        return val;
    }
}

edited Feb 11 '14 at 20:00

answered Feb 11 '14 at 04:19

Selman Genç

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...and make sure the namespace is included in your `using` statements if it isn't the same as the class where the extension is being used. – Erik Noren Feb 11 '14 at 04:19
1

@Selman22 It would not compile if that was not already the case. – Luc Morin Feb 11 '14 at 04:20
They might have defined the extension inside another instance class. It would compile but it wouldn't be detected as a proper extension method when it came to invoke it, if I remember correctly. – Erik Noren Feb 11 '14 at 04:22
Ok it was there, but not static. Thanks! Problem solved. Ill mark soon as its able. – user2292539 Feb 11 '14 at 04:22
Actually, when I try to define an extension method inside an instance class, I get a compile error "Extension method must be defined in a non-generic static class" – Luc Morin Feb 11 '14 at 04:27

Dictionary extension compiles but not callable

1 Answers1