CODEWITHSUNDEEP
c#genericscastingcovariance
jdphenix
jdphenix

Reputation: 15425

Cannot implicitly convert type from non-covariant generic interface

Important edit: Do not use a Dictionary in this context. It uses Object.GetHashCode() which isn't good for use as a dictionary key. I still learned something from this though.

I have the following declaration 

private static IDictionary<IDictionary<string,string>, IEnumerable<Fishtank>> _cache;

and the following code to attempt to initialize it

if (_cache == null) 
  _cache = new Dictionary<Dictionary<string,string>, LinkedList<Fishtank>>();

The problem I'm having is the initialization generates a compile time error.

Cannot implicitly convert type 'System.Collections.Generic.Dictionary,System.Collections.Generic.LinkedList>' to 'System.Collections.Generic.IDictionary,System.Collections.Generic.IEnumerable>'. An explicit conversion exists (are you missing a cast?)

I know that Dictionary and LinkedList implement IDictionary and IEnumerable respectively, so I'm at a bit of a loss here.

Upvotes: 1

Views: 715

Answers (1)

Damith
Damith

Reputation: 63065

you can do as below 

if (_cache == null) 
    _cache = new Dictionary<IDictionary<string, string>, IEnumerable<Fishtank>>();

Upvotes: 3

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