Re: How to avoid complex switches?

none <""mort\"@(none)">
Sun, 28 Mar 2010 22:55:53 +0200
Ian Collins wrote:

On 03/29/10 06:32 AM, none wrote:

I have a class that takes a few template parameters:

template<typename A, typename B, typename C,typename D>
class MyClass {
// ...

The types A,B,C and D are selected from a user specified input file
(properties file):

A = 1
B = 2
C = 1
D = 3

I then parse this file an need to create MyClass with the correct types:

<snip big ugly switch>

But this switch grows extremely large when the number of choices for
each type grows and is also very ugly/error prone. It could be nice if
it was possible to do something like this instead:

Could you use the factory pattern? If you create a polymorphic base for
MyClass, you can have simple factory objects:

struct MyClassFactoryBase
  virtual MyClassBase* build() = 0

template<typename A, typename B, typename C,typename D>
struct MyClassFactory : MyClassFactoryBase
  MyClass<A,B,C,D>* build() { ... }

You can yen populate a lookup table with MyClassFactory objects.

But I still need to parse the user specified selection into to the correct types, so I don't see how
you can avoid a switch with the above?

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