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

[Doug Gregor]

On 9/13/06, Douglas Gregor <doug.gregor@gmail.com> 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).

  Cheers,
  Doug
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