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Bug 269 - Create a header which properly forwards eigen types
Summary: Create a header which properly forwards eigen types
Alias: None
Product: Eigen
Classification: Unclassified
Component: Core - general (show other bugs)
Version: 3.0
Hardware: All All
: --- Unknown
Assignee: Nobody
Depends on: 339
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Reported: 2011-05-16 13:57 UTC by Benjamin Schindler
Modified: 2019-12-04 10:45 UTC (History)
3 users (show)


Description Benjamin Schindler 2011-05-16 13:57:29 UTC
To reduce compilation time, I'd like to have the possibility to forward-declare eigen types. Eigen got quite expensive nowadays:

bschindl@hundertwasser ~/documents $ cat test.cpp
#include <eigen3/Eigen/Core>
bschindl@hundertwasser ~/documents $ g++ -E -o test.cpp.o test.cpp 
bschindl@hundertwasser ~/documents $ wc -l test.cpp.o 
56644 test.cpp.o

So basically, 56k lines of code by including eigen only - that's a lot. Of course, quite a bit of it is shared (i.e. comes from stl headers but still). 

There is Eigen/src/Core/util/ForwardDeclarations.h, but eigen files are not self-contained unfortunately (i.e. to include it, I'd have to do: 

namespace Eigen { #include <....> }

but Eigen/Core does a lot more preprocessor stuff to make this just work, so currently there is no easy solution
Comment 1 Gael Guennebaud 2013-06-10 21:05:04 UTC
We had something like that at the beginning of Eigen, but in practice the gain on compilation times was really small. You can try by copying Eigen/Core and removing everything after ForwardDelcarations.h.

A better solution is to use precompiled headers. So I'd say wontfix.
Comment 2 Nobody 2019-12-04 10:45:03 UTC
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