I thought the whole idea of warnings was to let us know when we're doing something that's legal, but might have undesirable consequences

Actually, I agree with you that it might be nice to be (able to be) warned when we either define or import a name that clashes with a built-in. As I recall, there is a warning that says something to the effect of: "xyz may clash with a future keyword"; though I can't remember what triggers it.

Seems to me that clashing with an existing keyword is actually more important to know that some possible future event. And that if the "clashes with existing" warning was implemented, the "clashes with future" would be redundant; because if that eventuality ever came to pass, it would attract the "clashes with existing" in a timely fashion.

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In reply to Re^5: perl index function error when "use PDL" by BrowserUk
in thread perl index function error when "use PDL" by allori

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