When should we use Action<T> and not to define a delegate explicitly?
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TylerH
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amit kohan
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1Dupe: [creating-delegates-manually-vs-using-action-func-delegates](http://stackoverflow.com/questions/4482613/creating-delegates-manually-vs-using-action-func-delegates) – nawfal Jul 07 '14 at 16:48
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Well...
Action<T> is almost the same as delegate void (T t)
and
Func<T> is almost the same as delegate T ()
Action and Func (and lambdas) are just 'syntactical sugar' and a convenience for using delegates.
So it's really just a matter of preference.
Randy Minder
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@amitkohan Yes, _almost_ the same. One thing to be aware of is contravariance of `Action
`. If contravariance is not desired, write your own delegate type without contravariance. See my comment to Servy's answer. – Jeppe Stig Nielsen Nov 12 '12 at 12:02
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It's entirely a matter of preference, but I see no reason to ever define your own delegate if one of the overloads of Action or Func will work. If you have a ref/out/params parameter, optional arguments, or some other such edge cases you have no choice but to define your own.
Servy
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Something else: Since .NET 4.0, `Action
` is **contravariant** in `T`. But at the same time, delegate combination ("addition" of two delegate objects) doesn't work with contravariance (Lippert's words: [all messed up](http://stackoverflow.com/a/2307942/1336654)). So suppose you make a `public event Action – Jeppe Stig Nielsen Nov 12 '12 at 12:00ItHappened;`. Then because of contravariance, one subscriber could add an `Action -
While with Action/Func life is much easier, custom delegates give you better type safety (correctness). In the end there's a trade-off. Another benefit is the better (more meaningful) parameter name and IDE's documentation support. – nawfal Jul 07 '14 at 16:53