Re^3: Converting to number doesn't always work... (updated)

$x = \$r;

I am confused why you're taking this step? This means that $x is a reference, and a reference is like a dual-valued variable*: As a string, it's "SCALAR(0xabc)", which I would guess is what looks_like_number is looking at², and in numeric context, it's the memory address, which is why $x += 1 doesn't warn.

* Update: Triple-valued? It's a reference, string, and number ;-) (Or rather: It's a reference, that gets converted to different values depending on context.)

² Update 2: Hmmm, nope, looks like it's checking the flags in this case.

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Re^4: Converting to number doesn't always work... (updated) by syphilis (Archbishop) on Nov 22, 2019 at 12:18 UTC
I am confused why you're taking this step? Nothing insidious or profound. I read "this gives you the exact internal function that Perl uses to check strings and generate that warning in the first place" as implying both that: 1) if looks_like_number($x) returns true, then there will be no warning given when $x is used in numeric context; && 2) if looks_like_number($x) returns false, then a "non-numeric" warning will be given when $x is used in numeric context. I find it interesting that the latter of the two is not necessarily true - furthermore, I found it so interesting that I decided to provide an example where looks_like_number($x) returns false, yet no warning is issued when $x is used in numeric context. Your second update references the use of looks_like_number() in sv.c. Note that Scalar::Util::looks_like_number() is a different function. (That is, it doesn't simply wrap the perl API function of the same name ... it does some other stuff as well.) Cheers, Rob	[reply]
Re^5: Converting to number doesn't always work... by haukex (Archbishop) on Nov 22, 2019 at 13:04 UTC
Yes, I guess I was a little too unspecific* in what I wrote: Given a string `$x`, `looks_like_number($x)` should accurately report whether the warning will occur. Note that Scalar::Util::looks_like_number() is a different function. (That is, it doesn't simply wrap the perl API function of the same name ... it does some other stuff as well.) True, it's a different function - AFAICT, `Scalar::Util::looks_like_number` just adds get-magic to `Perl_looks_like_number` in `sv.c`, which in turn calls `Perl_grok_number` in `numeric.c`, if the scalar has a valid string component (`SvPOK`). And my understanding is that `grok_number` is the same internal function that is used to inspect strings for their numeric content - see e.g. `Perl_sv_2nv_flags` in `sv.c`, which is called by the `SvNV` macro, and which calls `not_a_number` to generate the "`Argument isn't numeric`" warning. I had done all this research in the past, and perhaps remembered it a little too simplified, thanks for poking me on this `:-)` * Update: Well, to nitpick: I did write "the exact internal function that Perl uses to check strings", and you didn't give it a string `;-P` But "exact" is indeed inaccurate.	[reply] [d/l] [select]
Re^6: Converting to number doesn't always work... by syphilis (Archbishop) on Nov 22, 2019 at 13:31 UTC
Well, to nitpick: I did write "the exact internal function that Perl uses to check strings" Actually, I did pick that up on a subsequent (but not first) reading of your post. But I decided to ignore that.... as to do otherwise was of absolutely no advantage to me ;-) Cheers, Rob	[reply]


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