Covariance, such as interface ia and its subclass AA.
IA & ltBaseQueryInfo & gta = new aa & ltmultiborowtag & gt (...)//Ok, correct covariation.
AA & ltBaseQueryInfo & gta = new aa & ltmultiborowtag & gt (...)//Error, covariation is not allowed!
Definition of covariant interface:
Interface IA & ltout T & gt// This out is very important, indicating that this interface supports covariation.
{
void F()； //ok
t G()； //Well, covariation allows generic parameters as return values.
void H(T T)； //Error, covariation does not allow generic parameters as function parameters.
}
Therefore, the solution 1: When declaring the DataTagEnumQueryDict variable, use the parent interface of DataProcessEntity that declares out instead. For example, suppose there is an interface idataprocess.
It is declared as:
Private static dictionary & ltDataTagEnum, idataprocess & ltbasequeryinfo & gt & gtdatatagenumquery dictionary = new. ...
Solution 2:
What if the class DataProcessEntity doesn't declare the parent interface of out at all? No way, we can only have new data processing entities.
Solution 3: If you don't want to be new? Data processing entity & ltBaseQueryInfo & gt{...}, what should I do? There is a more tortuous way:
Define your own interface!
Interface idataprocessentitydelegator < out T & gt
{
void AAA()； //Copy the method signature of DataProcessEntity to be used as it is, but never copy the method signature using t as the method parameter.
t BBB()；
....
}
redefinition
Principal of Class Data Processing Entity & ltT>
{
Private read-only data processing entity;
Principal of public data processing entity & ltout T & gt(A a, B b, C c ...)
{
Entity = New? Data processing entities (a, b, c ...);
}
public void AAA()= & gt； Entity. AAA()；
Public? t BBB()= & gt； ? Entity. BBB()； //Note: This is shorthand grammar after C#6.0, otherwise write a complete function body yourself.
}
Then, you can write code happily:
Private static dictionary & ltDataTagEnum,? IDataProcessEntityDelegator & lt； BaseQueryInfo & gt& gtDataTagEnumQueryDict = new ...
......
DataTagEnumQueryDict。 Add (..., data processing entity principal & ltbasequeryinfo & gt {...});
DataTagEnumQueryDict。 Add (..., data processing entity principal & ltmultiborowtag & gt {...}? );
DataTagEnumQueryDict。 Add (..., data processing entity principal < blacklist label > {...}? );
Which method to use depends on your consciousness.