Function Templates - Explicit specialisation vs Global Functions (C++)

Question

I know that Function Templates are used so as to make the functions portable and so that they could be used with any data types.

Also Explicit Specialization of templates is done if we have a more efficient implementation for a specific data type.

But then instead of Explicit Specialization we could also just code a Nontemplate Function which could be called from main . This would save us some processing time as the compiler would locate Nontemplate Functions faster than Explicitly Specialized Templated Functions which would in turn be better in terms of efficiency.

So why do we use Explicit Specialization when we have the alternative of just calling Nontemplate Functions?

Please correct me If I'm wrong!

Edit 1: I was told by my professor that whenever we make function templates and call the function from main ,the compiler first looks for a templated function and if its not able to locate that,then it searches for a function template from which it in turn makes a templated function and then calls for it.

Answer 1

It sounds like you're confusing compile-time efficiency with run-time efficiency. The choice of which function to call is made at compile time, not run time, so it will make no difference to the run time of the program.

Explicit Specialization is used when you have a special case that can benefit from special treatment. Sometimes this backfires, as in the case of std::vector<bool>, while other times it's quite handy. It means that the user of the function doesn't need to be aware that there's a special case; it's just transparent.

Answer 2

This would save us some processing time as the compiler would locate Global Functions faster than Explicitly Specialized Templated Functions which would in turn be better in terms of efficiency.

Why would the compiler find a nontemplate function faster than a function template specialization? Have you benchmarked compiler performance to verify this statement? If you use a function named f, the compiler always has to compile a set of candidate functions and perform overload resolution to determine the correct function to be used.

At runtime (which is when performance really matters, right?) the performance of calling a function template instantiation should be no better than the performance of calling a nontemplate function.

So why do we use Explicit Specialization when we have the alternative of just calling Global Functions?

In the general case, for function templates, you don't use explicit specialization, because it's usually confusing and difficult. The ISO C++ standard has a poetic warning to be extremely cautious when specializing function templates. You can read Herb Sutter's "Why Not Specialize Function Templates?" for a good explanation of the issues and why you don't want to specialize function templates.

Answer 3

For reasons of uniformity. The person using the API just calls methods with particular arguments, some get the generic function some get explicitly specialised functions - the client need neither know nor care which they use.