Jonathan M Davis:
Honestly, I would have considered that to be a bug. Converting the return type to a different level of mutability based on purity is one thing. Automatically casting the return value just because the function is pure is another matter entirely. Clearly, it can work, but it seems incredibly sloppy to me.
In foo1 D is working as designed, as this was a desired feature, it has passed the Kenji and Walter review, and it was implemented several months ago. It's a very handy way to create immutable data with pure functions and it's safe, it's safer than assumeUnique that is just a convention. Very recently Walter has further improved this feature, allowing more implicit conversion cases. So it's the opposite of a bug, it saves you from bugs in three different ways. But my question was about the successive foo functions :-) Bye, bearophile
