The rule that a failure of the template argument substitution is not an error—the SFINAE rule—had to be added to the language simply to make certain narrowly defined template functions possible. But the ingenuity of a C++ programmer knows no bounds, and so SFINAE was repurposed and exploited to manually control the overload set by intentionally causing substitution failures.
Let's consider in detail how SFINAE can be used to knock out an undesirable overload from the overload set. Note that, for most of this chapter, we will lean heavily on C++11 and, later, C++14 features. You may want to review these recent additions to the language; if so, please refer to the Further reading section at the end of this chapter.
