On Aug 12, 2007, at 1:22 PM, Ion Gaztañaga wrote:
John Maddock wrote:
The difference is that C++ lets you spot the duplication: for example if you discover that your application is using vector<int>, vector<unsigned>, vector<long> and vector<heaven-knows-what-else> then you should definately be asking why they can't all be using the same instantiation!
Just a curiosity, Digginig in the Freescale/MSL STL implementation we use at job I've seen an space optimization MACRO (I don't know if it's activated by default or not) where all vectors of POD types of the same size where treated with a single type type (just the same trick as vector<void*> but with ints, shorts, and similar POD types). I suppose that option was there because the compiler was not smart enough to optimize them (I don't know if that's true nowadays).
It's been awhile since I looked at the most recent Freescale STL, but last time I looked, this flag was on by default. This optimization was originally written before the Freescale linker did code folding. After the Freescale linker did code folding it appeared to me that the two optimizations worked together synergistically. I.e. sometimes the lib would catch stuff the linker missed and vice-versa. Fwiw, it isn't an easy optimization in the lib to get right (I got it wrong first time out of the gate). But it does seem worthwhile. I had a major customer once tell me this optimization saved him 750Kb code, and this was back when a Mb of code was a lot. ;-) -Howard