Hi There, While playing with generics (ref. class inheritance and type incompatibility), I have an idea to use "generic class helper" to overcome the problem that generic methods cannot be "virtual" (because the compiler see specialized class different than the generic one?)
I have a TTree generic class (ref: https://github.com/xrfang/fpcollection/blob/master/src/units/tree.pas), which currently has problem with the Clone method, I did the following: type generic TTree<T> = class ... ... end; TTreeType = class of TTree; TTreeHelper = class helper for TTreeType; The compiler does not compile because it thinks you cannot use a class reference (TTreeType) while defining a class helper. Why? Shouldn't class references has same effect as a Class? Ok, since it does not compile, I changed the last line to the following alternatives, but NONE of them compiles: 1) TTreeHelper = class helper for TTree; 2) generic TTreeHelper<T> = class helper for TTree<T>; My purpose is that since the Clone method cannot be virtual (because descendant class will not have same return type as the generic class), I try to write a class helper for ALL specialized TTree and their descendants. Of course I can (and will) follow Sven's advice in that email to modify my TTree class. This email is just two other questions: 1) is it possible to define class helper for generic classes? 2) why class helper require a class and we cannot use a class reference? Best Regards, Xiangrong
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