Re: [boost] [Review] Fusion

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2006-05-16 05:19:55

Douglas Gregor wrote:
>    pair: I tripped over the name of this entity a bit. It's a little
>    odd to have a "pair" with only one kind of data. I guess I'd feel
>    better if this were called "keyed_value" or "key_value", because
>    it's easier for me to copy with a typed key than it us for me to
>    have a pair that's very different from std::pair.

I had a similar feeling about the "half runtime pair" when reading the
documentation. After a deeper look and actually using the library, my
scepticism vanished, however, because:

1.

When writing Fusion algorithms there are in fact two control paths to 
take care about: the template instantiations and the runtime behaviour. 
I experienced that it makes sense to work out the compile time path 
first, which is the point where the data structures are chosen. 
In the compile time world, Fusion pairs are just pairs ;-).

Using "keyed_value" for e.g. the state with fusion::fold seems 
misleading to me, while using a "pair" makes a lot of sense.

2.

The only difference between the Fusion and STL pair concept is the 
'first' member variable. The current name reflects these conceptual
similarities.

Regards,

Tobias