Circumventing template specialization

问题

Suppose I am a user of a Certain Template Library (CTL) which defines a template, named, say, Hector

template <class T>
class Hector {...};

And in its documentation it gives many guarantees about Hector template behavior. But then it also defines a specialization for a certain type Cool

template <>
class Hector<Cool> {....};

The purpose of the specialization is a more optimized implementation of Hector, but unfortunately because of this optimization many guarantees of Hector are violated.

Currently I really don't need the optimization, I'd rather preserve all the guarantees of Hector. Is there any way I could, without changing the library code (CTL is a highly respectable library, you know), circumvent the specialization? Any way at all? Maybe write some sort of wrapper? Anything? I just want to the compiler to generate code for Hector<Cool> in a normal, non-optimized way, with all the guarantees.

回答1:

Are you able to use the related template Reque that doesn't have the undesired specialization? Otherwise I think you'd need to create a wrapper for Cool so that the specialization isn't used.

回答2:

You could wrap cool in a dummy type to prevent the template from specializing it.

回答3:

No. And even if it can be done in some esoteric fashion, don't. Circumventing language features should set off an alarm.

You have to wrap the value or use a different type like char instead of bool (they behave similarly), giving std::vector<char> instead of std::vector<bool>.

回答4:

Here's a little generic disguiser:

template <typename T>
struct Drool
{
  Drool(T d) : b(d) { }
  inline operator T() const { return b; }
  inline Drool<T> & operator=(T d) { b = d; return *this; }
private:
  T b;
};

Now you can say Hector<Drool<Cool>>.

Improved version according to Xeo:

template <typename T>
struct Drool
{
  Drool(const T & d) : b(d) { }
  Drool(Drool && o) = default;

  inline operator const T & () const { return b; }
  inline operator       T & ()       { return b; }

private:
  T b;
};

回答5:

Open the ~~standard~~ certain implementation
Ctrl+A
Ctrl+C
Create a new file called "my_hector.h"
Ctrl+V
Remove the specialisation
Search and replace #include <hector> with #include "my_hector.h"
[ Edit for @Xeo ;-) ]
Rename identifiers that begin with two leading underscores followed by a lowercase letter, and all identifiers that begin with a single leading underscore following by an uppercase letter.

来源：https://stackoverflow.com/questions/6499007/circumventing-template-specialization

标签

c++

templates

template-specialization