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Date: Wed, 27 Aug 2025 14:25:49 +0100
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Subject: =?US-ASCII?Q?Re=3A_=5BPHP-DEV=5D_=5BRFC=5D_Add?=
 =?US-ASCII?Q?_=22is=5Frepresentable=5Fas=5Ffl?=
 =?US-ASCII?Q?oat=28=29=22_and_=22is=5Frepresent?=
 =?US-ASCII?Q?able=5Fas=5Fint=28=29=22_functions?=
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

On 26 August 2025 19:23:20 BST, "Tim D=C3=BCsterhus" <tim@bastelstu=2Ebe> w=
rote:
>"Surprising changes" is not a meaningful term=2E Keep in mind that the be=
havior of the function will need to be accurately documented and that folks=
 need something to work with to determine whether a report is valid or not =
when bugs in the function get reported - which will inevitably happen=2E

I think there's a sliding scale of "strictness" of casts, with string to f=
loat probably the hardest to pin down=2E=20

At one end, you have "purely lossless" or "symmetrical" - where (string)(f=
loat)$x =3D=3D=3D $x This would mean accepting '4' but not '4=2E0', which i=
s probably not what users would expect=2E=20

From=20there, you can add some "normalisation" - ignore insignificant zeros =
at start and end; perhaps also ignore leading and trailing spaces=2E

Then you get alternative representations - most commonly, scientific notat=
ion like '2=2E5E10'=2E This hugely increases the number of inputs that resu=
lt in the same output, e=2Eg=2E '0=2E2E1' is yet another synonym for '2'=2E

Then there are inputs which don't fully match the normal format, but are u=
nambiguous - '=2E1', '1=2E', '+1', etc

At the other end of the scale, there's the "best guess" approach that PHP'=
s explicit cast operators use - (string)(float)'  +4=2E2E1 bananas ' result=
s in '42'

And that's *before* we check the precision of the resulting interpretation=
, and how close the floating point value is to the target decimal=2E

I'd really like something stricter than is_numeric but more flexible than =
ctype_digit; but exactly what it should do is a bit of a minefield=2E=20


Rowan Tommins
[IMSoP]