[swift-users] extension Dictionary where Key == MyStructType

[Dmitri Gribenko]

On Wed, Jan 27, 2016 at 12:16 PM, Darren Mo via swift-users
<swift-users at swift.org> wrote:
> I want to add a method to Dictionary but only if the key is a specific
> non-protocol type.
>
> I tried:
> extension Dictionary where Key == MyStructType
>
> This yields “error: same-type requirement makes generic parameter 'Key'
> non-generic”.
>
> Is there a way to do this that doesn’t involve subclassing Dictionary?

There is a workaround that involves adding an otherwise a useless
protocol.   I leave it up to you to decide whether it is worth it.

protocol DictionaryType {
  typealias Key
  typealias Value
}

extension Dictionary : DictionaryType {}

extension DictionaryType where Key == MyStructType { ... }

Dmitri

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