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Re: C++ PATCH: PR 20599 (1/3)

On 9/13/06, Douglas Gregor <> wrote:
Several of the facilities in the C++ Library TR1 just can't be
implemented well without variadic templates. Our current
implementation uses some disgusting, barely-maintainable preprocessor
metaprogramming to give a poor approximation of these libraries.
Variadic templates will help us improve compile times, simplify the
code, and provide a more flexible TR1 implementation than any other
compiler can.

More motivation for variadic templates is attached. This chart shows the compilation times for a simple program that includes all of the function objects and tuples parts of libstdc++'s TR1. We vary the maximum number of supported arguments from 3 to 40 (libstdc++ currently supports a maximum of 10), using evil preprocessor tricks.

I meant to go up to 100 arguments supported, but I run out of memory
on my Mac (that has 3.5MB RAM).

I do not have the complete variadic templates implementation to
compare against, but it should be faster than the 3-argument version
(under 1 second).


Attachment: ct_performance.png
Description: PNG image

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