CODEWITHSUNDEEP
c++templates
user173342
user173342

Reputation: 1840

Variable of a template class with a template class template parameter set to a base template of the derived template with the variable

I'm attempting to have a derived class (normal template) that has a variable of a template type that has as its template class parameter the type of a base class (normal template, same parameter as the derived class) of the derived class (the one with the variable). This makes VC++ incredibly angry at me, and I am incapable of calming its fury. Here's a quick example:

template<template<typename VT> class CT, typename VT> struct encapThing {};

template<typename VT> struct innocuousBase {};

template<typename VT> struct derivOfDoom : public innocuousBase<VT>
{
    encapThing<innocuousBase, VT> ohgodhelp; //C3200
};

It will throw a C3200, saying it expected a class template. Now, I can see why this might be thinking there is a recursive loop of templates within templates, even if this isn't actually the case. How can I convince VC++ otherwise?

Upvotes: 13

Views: 200

Answers (1)

ildjarn
ildjarn

Reputation: 62985

Unqualified use of innocuousBase inside of derivOfDoom<> is interpreted as innocuousBase<VT>, much as unqualified use of derivOfDoom in that context would be interpreted as derivOfDoom<VT>. I don't remember offhand whether or not this is standard-conformant behavior, but the workaround is trivial: fully qualify innocuousBase so the compiler knows you're referring to the innocuousBase class template and not the innocuousBase<VT> base class:

template<typename VT> struct derivOfDoom : innocuousBase<VT>
{
    encapThing<::innocuousBase, VT> ohgodhelp;
};

Upvotes: 4

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