Casting System.Func <T>
I am redistributing code that uses the following construct. What I would like to do is make it generic so that I can have other types of parameters in Func.
IDictionary<string, Func<Employee, string>>
I tried using:
IDictionary<string, Func<Object, string>>
Then return it:
(IDictionary<string, Func<Object, string>>)myDictionary
But I am getting an exception saying that I cannot use
Unable to pass object of type 'System.Collections.Generic.Dictionary
2[System.String,System.Func
2 ...
I have been playing with generics, but it seems to me that I still cannot set and generic field in my class
private IDictionary<string, Func<T, string>> lineSpecification;
Looped around so any pointers would be appreciated.
EDIT:
This is the complete error message I am getting:
System.InvalidCastException : Unable to cast object of type 'System.Collections.Generic.Dictionary`2[System.String,System.Func`2[DataObjects.Employee,System.String]]' to type 'System.Collections.Generic.IDictionary`2[System.String,System.Object]'.
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Instead, enter the dictionary like
IDictionary<string, object>
and enter the resulting value:
IDictionary<string, object> myDictionary = new Dictionary<string, object>();
var myDelegate = (Func<Employee, string>)myDictionary["my employee delegate"];
Of course, this will fail if you try to use the wrong Func type, so you need to be sure to know which keys map to Func types.
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It sounds like you want your dictionary to have different types of values; in other words, that one dictionary can contain Func<Employee, string>
and Func<Customer, string>
.
If so, then you basically have no choice but to use a common base type for the type argument TValue
and discard delegates when you retrieve them from the dictionary. The general base type can be System.Delegate
or System.Object
.
(There are actually other options besides this, but they just push casting to a different part of the design. For example, you could write a wrapper class that handles casting for you. Such solutions usually don't apply, don't settle for a cost-benefit analysis.)
My dictionary will only store the same type, but in different scenarios I want it to be able to store different types. The problem I am having is casting from Func to Func throws a casting exception.
In this case, it is not clear why you want to have Dictionary<string, Func<Object, string>>
and not Dictionary<string, Func<Employee, string>>
. If any given dictionary will only contain one delegate type, then create the dictionary accordingly:
Dictionary<string, Func<Employee, string>> dict = new Dictionary<string, Func<Employee, string>>();
If the dictionary is a member of a generic class or a local variable or parameter of a generic method, you can use type parameters in the dictionary declaration:
class Processor<T>
{
void Process(T value, Dictionary<string, Func<T, string>> functions) { //... }
}
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