Templates

• Stroustrup says
  • Templates are the basis for generic programming in C++
  • He defines generic programming as
    • Writing code that works with a variety of types presented as arguments, as long as those argument types meet specific syntatic and semantic requirements.
  • A great example is the standard algorithm library, and teh standard container classes.
    • You can find the min of whatever you want as long as it supports <
    • Look at the definition at c++.com
• For functions the format is

  • template < class identifier [, class identifier...]> function_declaration;
    template < typename identifier [, typename identifier ... ]> function_declaration; 

  • Either class or typename are acceptable.
• Stroustrup says that the compiler "looks into" the template
  • And if it can find anything to match, it will
  • If it finds a matching template, it will then "generate the code" for for the type given.
  • To do this, it needs access to all of the code.
  • Therefore we put templates in .h files.
  • This is a convention, not a requirement.
  • Stroustrup seems to hope that there will be a better solution some day.
• Take a look at Smallest.h
• You can also build a templated class.
  • I have built a MyListT.h list class.
  • Note the use of MyNode<T> * tmp
    • But this is normal
    • vector < int> for example.
    • Note the use of T rv{} in the Data function.
• Stroustrup says
  • Templates add flexibility
  • And they have nearly optimal performance
  • But they have poor "separation" of interface and implementation.
  • And the error messages are problematic.
• The compiler does not build all class methods uless they are needed.
  • I just had strange situation where I had a method with a syntax error, but I didn't see it until much later because I did not use that method.