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0 pointsjcelerier4y ago0 comments

Inlining the ctable into the object would only be faster if

- you have very few objects

- you have very few virtual functions

If you have a lot of objects or a lot of virtual functions, things will be less likely to fit in cache which will entirely destroy your performance, by an order of magnitude when compared to a mostly-always-branch-predicted indirection.

I remember experimenting with a an "inlined" version of std:: function and just having inlined the 5 ctor/move ctor/copy ctor/assignment operators was already slower than the vtable version when going through hundreds of callbacks ; imagine for something like Qt where QWidget or QGraphicsItem have 20+ virtual methods.

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rurban4y ago

Depends. My STL in C is faster by inlining the iterator methods. With something like glib or qt double indirection would be better of course, because these can be shared then.

In my jitted ruby-like VM my methods are also copied, not referenced. Javascript also prefers copying the methods. This is usually called prototype-based OO. True prototypes copy the struct fields also, without creating classes, but copying the read-only methods only is a worthwhile OO optimization, C++ cannot do.

jcelerierOP4y ago

Can you share some benchmarks for your STL ?

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