Cast to IDictionary

Question

The function below returns a type of Dynamic, what is the most efficient way to cast it to IDictionary

 public dynamic GetEntities(string entityName, string entityField)

Is there a reason you can't use `var dictionary = (IDictionary)GetEntities(...);`? — Daniel Hilgarth, Nov 28 '12 at 14:40
What are the type-parameters of the dictionary? `IDictionary`? — looper, Nov 28 '12 at 14:41
@user1842828 Who knows what's behind the `dynamic`-typed object...? And, after all, this wouldn't be a cast but a **conversion** — Matías Fidemraizer, Nov 28 '12 at 14:42
If you safely know you have an IDictionary, why use dynamic at all? — Joel Coehoorn, Nov 28 '12 at 14:45
Matías Fidemraizer wrote the problem. Could you *please* post the code of `GetEntities`? — looper, Nov 28 '12 at 14:46
I'm assuming this is related to this previous question: http://stackoverflow.com/questions/13592065/convert-type-system-dynamic-dynamicobject-to-system-collections-ienumerable — Paolo Moretti, Nov 28 '12 at 14:48

David Hoerster · Accepted Answer · 2012-11-28T15:01:45.903

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I'd probably go with the as operator.

var result = GetEntities("blah", "blahblah") as IDictionary<string,string>;

Then do a null check.

UPDATE

In regards to the "efficient" part of your question, I think as may be pretty efficient compared to some other paths you could take:

You could just blindly cast it to IDictionary<string,string> and then catch the exception, but using exceptions for control flow isn't a good idea and is expensive.
You could use a convention like expression is type ? (type)expression : (type)null, but in this case, you evaluate expression twice (but you do get a null if the expected type isn't the type that expression returns). So you're doing double evaluations.
as is only good for reference or boxing conversions, not to perform user-defined conversions, so if you need that, then as isn't for you.

See this article on MSDN.

UPDATE 2

I made an assumption on the key/value types of the IDictionary. You could just use IDictionary after as instead of specifying the generic type parameters. I guess it depends on what you're expecting.

Hope this helps.

edited Nov 28 '12 at 15:01

answered Nov 28 '12 at 14:39

David Hoerster

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are you sure underling type of dynamic is dictionary? – Arsen Mkrtchyan Nov 28 '12 at 14:40
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@ArsenMkrt: No, that's why he is using `as` in the first place. – Daniel Hilgarth Nov 28 '12 at 14:40
But, think he want to convert to dictionary, any dynamic type, like [propertyname, value], agree the question doesn't clarify this part – Arsen Mkrtchyan Nov 28 '12 at 14:43
I made an assumption based on the input types to the OP's method. – David Hoerster Nov 28 '12 at 14:43

score 0 · Answer 2 · answered Nov 28 '12 at 14:39

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var dict = GetEntities(entityName, entityField) as IDictionary

or

var dict = GetEntities(entityName, entityField) as IDictionary<string,string>

answered Nov 28 '12 at 14:39

Tilak

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are you sure underling type of dynamic is dictionary? – Arsen Mkrtchyan Nov 28 '12 at 14:40
it has to be assumed. Otherwise type check will be needed first – Tilak Nov 28 '12 at 14:41
@user1842828 If you do the above check for dict != null before invoking any members from it or you'll get a null exception if the cast fails. – Rob Nov 28 '12 at 14:41
@ArsenMkrt: You are using `as` when you are **not** sure that the object has the expected type. – Daniel Hilgarth Nov 28 '12 at 14:42
as I said, I think question mean to convert any dynamic to dictionary like propertyName, Value. but it is not clear – Arsen Mkrtchyan Nov 28 '12 at 14:45

score 0 · Answer 3 · answered Nov 28 '12 at 14:40

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This way:

IDictionary dictionary = GetEntities("", "") as IDictionary;

Then either dictionary will be your object, or it will be null - depending on result type of GetEntities.

answered Nov 28 '12 at 14:40

AgentFire

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score 0 · Answer 4 · answered Nov 28 '12 at 14:40

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IDictionary dict = GetEntities(name, field) as IDictionary;

Then check for null and everything's fine. If you don't want that dict is null, but it throws an exception instead, use

IDictionary dict = (IDictionary) GetEntities(name, field);

answered Nov 28 '12 at 14:40

looper

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score 0 · Answer 5 · answered Nov 28 '12 at 14:40

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try this:-

 var dict = GetEntities(entityName, entityField) as IDictionary<string,string>

answered Nov 28 '12 at 14:40

Rahul Tripathi

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What if the types aren't ``? – looper Nov 28 '12 at 14:42
OP has provided the type as ? Is this wrong or am I am missing something? – Rahul Tripathi Nov 28 '12 at 14:43
Actually, no. He just wrote that it's a dictionary, the `string`s are only given as parameters in the function ;). – looper Nov 28 '12 at 14:45
@looper:- Then probably IDictionary dict = (IDictionary) GetEntities(name, field); will work great. But I still think that my answer will resolve OP's query!! – Rahul Tripathi Nov 28 '12 at 14:46
You don't even know that the `dynamic` object is actually a dictionary, let alone what the generic arguments of it might be. – Servy Nov 28 '12 at 15:05

Arsen Mkrtchyan · Answer 6 · 2012-11-28T14:47:59.010

It really depends what is the underling type of dynamic

If it is converted to dynamic from IDictionary, you can simply cast it

var dict = GetEntities(entityName, entityField) as IDictionary

if not, things become complicated, and it is not always possible to do

In this case you first need to check underling type by calling GetType method, if it is managed type and not DynamicObject, you are lucky, use reflection, if it is DynamicObject, I don't think there is any way to convert it to dictionary, because it may have custom implementation and even reflection doesn't work in this case

Cast to IDictionary

6 Answers6