Delegates: Predicate vs. Action vs. Func

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  • Predicate: essentially Func<T, bool>; asks the question “does the specified argument satisfy the condition represented by the delegate?” Used in things like List.FindAll.

  • Action: Perform an action given the arguments. Very general purpose. Not used much in LINQ as it implies side-effects, basically.

  • Func: Used extensively in LINQ, usually to transform the argument, e.g. by projecting a complex structure to one property.

Other important delegates:

  • EventHandler/EventHandler<T>: Used all over WinForms

  • Comparison<T>: Like IComparer<T> but in delegate form.

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