Examples of functional or dynamic techniques that can substitute for object oriented Design Patterns

Question

This is somewhat related to Does functional programming replace GoF design patterns?

Since the introduction of lambdas and dynamics in C#, are there any of the standard design patterns that could be considered obsolete or solved in some other way using lambdas or other language features?

For example, the dynamic features of C# can now be used to do multi methods. http://achoiusa.wordpress.com/2009/08/27/exploring-c-4-0-multimethods/ (I think Marc Gravell had some post about this to ?)

Personally I tend to do factories using Func of T nowdays.

e.g.

public static class SomeFactory
{
     public static Func<IUnitOfWork> GetUoW = 
       () => new EF4UoW(new SomeModelContainer());
}

// usage

var uow = SomeFactory.GetUoW();

// testabillity

var testUoW = new InMemUoW();
testUoW.Add(new Customer()...);

SomeFactory.GetUoW = () => testUoW;

// the service can get an UoW using the factory
var result = SomeDomainService.DoStuff(...);

Anyone got other examples?

[Edit] Ofcourse the patterns don't go obsolete per se but some patterns are paradigm specific and thus since C# is now multi paradigm, some of the functional properties of C# may make some of the OOP patterns less attractive.

score 8 · Accepted Answer · answered Apr 13 '11 at 08:27

8

Design patterns do not become obsolete just because a single language evolves. Patterns are usually language-agnostic.

In a sense you could say that .NET made the Observer pattern 'obsolete' already in .NET 1.0. However, that's not really correct because the pattern didn't become obsolete - the framework just provides a default implementation of the pattern, which means that you rarely have to implement it yourself.

In the same sense you can say that delegates are just anonymous interfaces, so a Func<T> is an Abstract Factory.

Patterns don't go away just because a language supplies idiomatic support for them.

answered Apr 13 '11 at 08:27

Mark Seemann

225,310
48
427
736

1

>> "Patterns are usually language-agnostic" , not quite, OOP and FP languages have different patterns.. – Roger Johansson Apr 13 '11 at 08:39
1

@Roger Alsing: OOP and FP are not languages, but rather paradigms. Agreed that they have different patterns, but within a paradigm the patterns are *usually* language-agnostic. – Mark Seemann Apr 13 '11 at 09:11
yes I just wanted to point out that "language agnostic" is a too broad, "language agnostic within a paradigm" is more correct IMO. and thus, if one paradigm solves a problem that another paradigm needs a pattern for, then one could argue that the pattern is no longer needed in a language which supports both paradigms.. – Roger Johansson Apr 13 '11 at 09:16

score 2 · Answer 2 · answered Apr 13 '11 at 08:27

Examples of some of the patterns which are provided as part of .net or C# that are not implemented explicitly by the programmer. I am providing answer with respect to .net in general and not specific to C#

Iterator patterns: By using a List<> or Collection<> developer gets the implementation of IEnumerable by default. So, explicit implementation is not needed. But having said that, there is someone (in this case, .net framework) who is implementing the pattern for the developer.

OOAD Design patterns do not become obsolete but developer need not know the implementation to use such patterns.

Object.Clone() is another example - prototyping. Developer need to just implement shallow or deep copy based on the requirement. But .net framework guarantees to support prototype pattern.
Decorator - with XAML, you can decorate a UI control with additional responsibilities. A text box can be decorated with border color, width & so on.
Tunneling and bubbling of events is an example of Chain or responsibility pattern
Events are first class citizens in .net and need not be implemented from scratch. This is an example of Observer pattern which programmer can use without implementing from scratch.

score 1 · Answer 3 · answered Mar 10 '15 at 02:21

1

Of course, the obvious one would be the Strategy Pattern, which can also be done with Higher Order Function.

answered Mar 10 '15 at 02:21

Shinji Nishizono

121
1
2

score 1 · Answer 4 · edited May 23 '17 at 10:34

1

You have the Visitor pattern as it's described in this answer :

Inheritance and service class

edited May 23 '17 at 10:34

Community

1
1

answered Apr 13 '11 at 08:24

remi bourgarel

9,231
4
40
73

Examples of functional or dynamic techniques that can substitute for object oriented Design Patterns

4 Answers4