Question

Suppose I have a set of functions and classes which are templated to use single (float) or double precision. Of course I could write just two pieces of bootstrap code, or mess with macros. But can I just switch template argument at runtime?

Answer 1

No, you can’t switch template arguments at runtime, since templates are instantiated by the compiler at compile-time. What you can do is have both templates derive from a common base class, always use the base class in your code, and then decide which derived class to use at runtime:

class Base {    ... };  template <typename T> class Foo : public Base {     ... };  Base *newBase() {     if(some condition)         return new Foo<float>();     else         return new Foo<double>(); } 

Macros have the same problem as templates, in that they are expanded at compile-time.