[Dune] ParameterTree

[Jö Fahlke]

Am Fri, 28. Jan 2011, 00:50:28 +0100 schrieb Carsten Gräser:
> Dear Dune,
> for for historical reasons ParameterTree contains
> 
>   int    ParameterTree::get(const string& key, int default);
>   double ParameterTree::get(const string& key, double default);
> 
> and the new methods with template parameter
> 
>   template<class T>
>   T ParameterTree::get(const string& key, const T& default);
> 
> IMHO we should removed the non-template methods since for
> key=0.1 you have the really ugly behaviour
> 
>   get("key", 1.0) == 0.1
>   get("key", 1)   == 0
> 
> due to the internal usage of atoi(). With the newer template methods
> you get an exception in this case since they use streams for conversion.

Seconded.  We should probably drop the overload for std::string as well (but
we should keep the one for char*).

> However the essential problem persists since the implicitly derived
> conversion type might not be what you expected. For example for key=1
> you have
> 
>   char defaultValue=0;
>   get<int>("key", defaultValue) == 1
>   get     ("key", defaultValue) == 49
> 
> In order to avoid this I suggest to forbid implicit determination
> of the template argument using
> 
>   template<class T>
>   struct DefaultType
>   { typedef T type };
> 
>   template<class T>
>   T ParameterTree::get(const string& key, const DefaultType<T>::type& default);

Objection.

I always understood the implicit determination of the conversion type as the
official way to select the particular overload of the get()-method with
default parameter, and I'm using it extensively.  The simple fact that these
methods were sometimes implemented as overloads made this the only reliable
way.  I consider The fact that most of these overloads are provided by a
method template an implementation detail.

Instead I propose specialize the ParameterTree::Parser struct for char to read
a numerical value instead of a character.

Bye,
Jö.

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