constexpr and CTFE

[bearophile]

This first question is mostly for D.learn, but below I show a partially related link too, so I put both of them here.

If you have library code, and the users of your library run one of your functions at compile time, later if you change your function it may not run at compile time any more. So isn't the quality of being able to run at compile time part of the signature of the function?

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GCC 4.6 implements the C++0x constexpr. I've found a note about constexpr, that touches the topic of logic const too, purity, memoization:

http://stackoverflow.com/questions/4748083/when-should-you-use-constexpr-capability-in-c0x/4750253#4750253

Bye,
bearophile