What are the true benefits of ExpandoObject

Question

The ExpandoObject class being added to  NET 4 allows you to arbitrarily set properties onto an object at runtime   Are there any advantages to this over using a Dictionary lt string  object gt   or really even a Hashtable   As far as I can tell  this is nothing but a hash table that you can access with slightly more succinct syntax   For example  why is this   dynamic obj   new ExpandoObject    obj MyInt   3  obj MyString    Foo   Console WriteLine obj MyString     Really better  or substantially different  than   var obj   new Dictionary lt string  object gt     obj  MyInt     3  obj  MyString      Foo    Console WriteLine obj  MyString       What real advantages are gained by using ExpandoObject instead of just using an arbitrary dictionary type  other than not being obvious that you re using a type that s going to be determined at runtime

User · Answer

Interop with other languages founded on the DLR is  1 reason I can think of  You can t pass them a Dictionary lt string  object gt  as it s not an IDynamicMetaObjectProvider  Another added benefit is that it implements INotifyPropertyChanged which means in the databinding world of WPF it also has added benefits beyond what Dictionary lt K V gt  can provide you

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Since I wrote the MSDN article you are referring to  I guess I have to answer this one   First  I anticipated this question and that s why I wrote a blog post that shows a more or less real use case for ExpandoObject  Dynamic in C  4 0  Introducing the ExpandoObject    Shortly  ExpandoObject can help you create complex hierarchical objects  For example  imagine that you have a dictionary within a dictionary   Dictionary lt String  object gt  dict   new Dictionary lt string  object gt     Dictionary lt String  object gt  address   new Dictionary lt string object gt     dict  Address     address  address  State      WA   Console WriteLine   Dictionary lt string object gt  dict  Address     State       The deeper is the hierarchy  the uglier is the code  With ExpandoObject it stays elegant and readable   dynamic expando   new ExpandoObject    expando Address   new ExpandoObject    expando Address State    WA   Console WriteLine expando Address State     Second  as it was already pointed out  ExpandoObject implements INotifyPropertyChanged interface which gives you more control over properties than a dictionary   Finally  you can add events to ExpandoObject like here   class Program      static void Main string   args              dynamic d   new ExpandoObject               Initialize the event to null  meaning no handlers         d MyEvent   null             Add some handlers        d MyEvent    new EventHandler OnMyEvent          d MyEvent    new EventHandler OnMyEvent2              Fire the event        EventHandler e   d MyEvent          e  Invoke d  new EventArgs              static void OnMyEvent object sender  EventArgs e              Console WriteLine  OnMyEvent fired by   0    sender            static void OnMyEvent2 object sender  EventArgs e              Console WriteLine  OnMyEvent2 fired by   0    sender            Also  keep in mind that nothing is preventing you from accepting event arguments in a dynamic way  In other words  instead of using EventHandler  you can use EventHandler lt dynamic gt  which would cause the second argument of the handler to be dynamic

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It s example from great MSDN article about using ExpandoObject for creating dynamic ad-hoc types for incoming structured data  i e XML  Json     We can also assign delegate to ExpandoObject s dynamic property   dynamic person   new ExpandoObject    person FirstName    Dino   person LastName    Esposito    person GetFullName    Func lt String gt        gt       return String Format   0    1         person LastName  person FirstName         var name   person GetFullName    Console WriteLine name     Thus it allows us to inject some logic into dynamic object at runtime   Therefore  together with lambda expressions  closures  dynamic keyword and DynamicObject class  we can introduce some elements of functional programming into our C  code  which we knows from dynamic languages as like JavaScript or PHP

User · Answer

var obj   new Dictionary lt string  object gt       Console WriteLine obj  MyString       I think that only works because everything has a ToString    otherwise you d have to know the type that it was and cast the  object  to that type     Some of these are useful more often than others  I m trying to be thorough    It may be far more natural to access a collection  in this case what is effectively a  dictionary   using the more direct dot notation  It seems as if this could be used as a really nice Tuple  You can still call your members  Item1    Item2  etc    but now you don t have to  it s also mutable  unlike a Tuple  This does have the huge drawback of lack of intellisense support  You may be uncomfortable with  member names as strings   as is the feel with the dictionary  you may feel it is too like  executing strings   and it may lead to naming conventions getting coded in  and dealing with working with morphemes and syllables when code is trying understand how to use members  -P Can you assign a value to an ExpandoObject itself or just it s members  Compare and contrast with dynamic dynamic    use whichever best suits your needs  I don t think dynamic dynamic   works in a foreach loop  you have to use var  but possibly you can use ExpandoObject  You cannot use dynamic as a data member in a class  perhaps because it s at least sort of like a keyword  hopefully you can with ExpandoObject  I expect it  is  an ExpandoObject  might be useful to label very generic things apart  with code that differentiates based on types where there is lots of dynamic stuff being used      Be nice if you could drill down multiple levels at once   var e   new ExpandoObject    e position x   5  etc      Thats not the best possible example  imagine elegant uses as appropriate in your own projects   It s a shame you cannot have code build some of these and push the results to intellisense  I m not sure how this would work though   Be nice if they could have a value as well as members   var fifteen   new ExpandoObject    fifteen   15  fifteen tens   1  fifteen units   5  fifteen ToString      fifteen   etc

User · Answer

After valueTuples  what s the use of ExpandoObject class  this 6 lines code with ExpandoObject   dynamic T   new ExpandoObject    T x   1  T y   2  T z   new ExpandoObject    T z a   3  T b  4    can be written in one line with tuples   var T    x  1  y  2  z   a  3  b  4      besides with tuple syntax you have strong type inference and intlisense support

User · Answer

The real benefit for me is the totally effortless data binding from XAML   public dynamic SomeData   get  set           SomeData WhatEver    Yo Man             lt TextBlock Text   Binding SomeData WhatEver     gt

User · Answer

There are some cases where this is handy  I ll use it for a Modularized shell for instance  Each module defines it s own Configuration Dialog databinded to it s settings  I provide it with an ExpandoObject as it s Datacontext and save the values in my configuration Storage  This way the Configuration Dialog writer just has to Bind to a Value and it s automatically created and saved   And provided to the module for using these settings of course   It  simply easier to use than an Dictionary  But everyone should be aware that internally it is just a Dictionary   It s like LINQ just syntactic sugar  but it makes things easier sometimes   So to answer your question directly  It s easier to write and easier to read  But technically it essentially is a Dictionary lt string object gt   You can even cast it into one to list the values

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I think it will have a syntactic benefit  since you ll no longer be  faking  dynamically added properties by using a dictionary   That  and interop with dynamic languages I would think

User · Answer

One advantage is for binding scenarios   Data grids and property grids will pick up the dynamic properties via the TypeDescriptor system   In addition  WPF data binding will understand dynamic properties  so WPF controls can bind to an ExpandoObject more readily than a dictionary   Interoperability with dynamic languages  which will be expecting DLR properties rather than dictionary entries  may also be a consideration in some scenarios

User · Answer

It s all about programmer convenience  I can imagine writing quick and dirty programs with this object

[c#] What are the true benefits of ExpandoObject?

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