CODEWITHSUNDEEP
c#.netgenerics
trialgod
trialgod

Reputation: 302

Generic Callbacks in C#

I want to write a wrapper for the System.Web.Caching.Cache, which handles my cache requests.

I need a method, which can invoke a callback method, if the cache entry doesn't exist. The problem is: I dont know how many params the callback method has:

public T Get<T, TCallback>(string key, TCallback func) where TCallback : Func<T>
{
    // check cachekey, do sth
    T result = func.Invoke();
    return result;
}

With this implementation it's possible to give a callback without params. But what if I have some?

Thanks, trial

Upvotes: 0

Views: 696

Answers (2)

Servy
Servy

Reputation: 203832

This method should only accept the parameters that this implementation wants to send to a given function. If it has no information that would be relevant to such a callback then it should simply require a parameter-less delegate. If it has parameters that will be needed for some, but won't be needed for others, it should provide them in all cases, using a single delegate.

It then becomes the responsibility of the caller to match the function that they want to call with the signature of the delegate. If they want to fix values for some function that has parameters your callback doesn't have, or if they want to call a function with less parameters, etc. it is their responsibility to make the "conversion", rather than this method's responsibility to deal with a delegate with an unknown signature.

The use of lambdas makes "converting" functions very easy; much easier than the alternative. To fix a value for a parameter when your callback doesn't have one, you can close over the variable:

int value = 5;
Get("key", () => SomeMethod(value));

You can also use a lambda to ignore a parameter:

Get("key", someParameterToIgnore => AnotherMethod());

Upvotes: 3

Vyacheslav Yudanov
Vyacheslav Yudanov

Reputation: 451

1) You can use dynamic or Dictionary as parameter of your callback. Put in Dictionary or dynamic string value - like CallbackType. Its bad because you lost static type analysing, but it possible.

2)It may be useful: Ellipsis notation in C#?

Upvotes: 0

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