[boost] [flyweight] key value with objects not constructible from a key

Subject: [boost] [flyweight] key value with objects not constructible from a key
From: Michael Marcin (mike.marcin_at_[hidden])
Date: 2008-11-11 15:57:29

The flyweight factory concept seems to be missing a key part of the GoF 
Flyweight pattern's FlyweightFactory participant. The GoF factory 
supplies the flyweight if one exists. This is what the current boost 
flyweight Factory concept does. If no flyweight exists the GoF flyweight 
factory creates one. In the boost flyweight library this functionality 
is somewhere else that doesn't seem to be described in the documentation.

The name factory for what is currently in place is misleading. Isn't it 
really just an associative container?

I'm trying to use flyweight to represent texture objects right now. 
These are surely a good candidate for use with flyweight as they are one 
of the examples given. My textures are fairly simple objects, with low 
coupling. Creating a texture is however expensive and has a lot of 
dependencies (libjpeg,libpng,etc). I typically have a TextureFactory 
which decouples the construction of a texture from the actual texture 
object and allows the work required to setup the various libraries to 
read images to be reused by all textures constructed from the same 
TextureFactory instance.

It doesn't seem possible to have this decoupling with flyweight.
Am I missing something?

-- 
Michael Marcin