March 01, 2003
C++ Expression Templates
March 2003/C++ Expression Templates
Creator Functions
Creator functions are a widely used technique in conjunction with template
programming. There are many examples of creator functions in the STL (e.g.,
make_pair). Creator functions are convenience functions that take advantage
of the fact that the compiler automatically deduces the function templates’
type arguments, while no such automatic deduction exists for class templates.
Each time you create an object of a type that is generated from a class template, you must specify the entire generated type name including all template type arguments. Often, these generated type names are very long and difficult to read and comprehend. Creator functions make life as a template user a lot easier: a creator function creates an object of a type that is generated from a class template without requiring that we type in very long type names.
More precisely, creator functions are function templates, which have the same
template type arguments as the class template that describes the type of the
object that is to be created. In a way, a creator function is similar to a constructor:
the arguments that you pass to a creator function are exactly the arguments
that you would otherwise pass to the constructor of the object that is to be
created. Since the compiler performs automatic template argument deduction for
function templates, you need not specify all the template arguments when calling
a creator function; the compiler will deduce them from the arguments passed
to the creator function.
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