This is a good point. Maybe some explanations help to clear the
confusion.
The method CharacterArray>>asNumber is more like a scanning
utility to return the next
literal number in the string (a
Fraction is not literal). It tries to scan a number without
considering that the contents of the string could be compiled and
evaluated to something that is a number. Effectively, the scanning
expects an optional negative sign, then digits, then optional
exponent notation (e.g. '-1e5' asNumber => 1.0e5). Even an
optional plus sign is not supported, although '+1' seems so clearly
a good number. That's the reason why #asNumber gives up as soon as
it sees the first character in '(1 / 2)' and return zero. Even for
the simple '(1)' #asNumber returns zero.
The same explanation helps for #readFromString:. If the receiver is
Number or any of its subclasses, then the concrete implementation
delegates to Number class>>readFrom: and Number
class>>readSmalltalkSyntaxFrom: which is effectively the
"same" what #asNumber does. The example '1/2' returns one because
the #asNumber scan stops at the '/', since it's neither minus nor
digit nor exponent.
The difference between Object class>>readFromString: and
Number class>>readFromString: is that Object class uses the
Compiler for a full translation and evaluation of the given string.
The standard for converting number IS Number
class>>readFromString: or #readFrom:. You can also look what
PrintConverter>>convertToNumber: does. But all those
mechanisms handle literal numbers only, not Fraction.
btw: It's a good idea to browse through number printing protocol
because there are differences in printing numbers for users or for
program internal purposes. For instance the FixedPoint 1.0 has
#printString = '1.0s' and for users you might want '1.00'.
Regards
Holger Guhl
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Georg Heeg eK Dortmund
Handelsregister: Amtsgericht Dortmund A 12812
Am 19.03.2013 12:10, schrieb Georg Heeg:
Interestingly
Object readFromString: '(1/2)' => (1 / 2)
Object readFromString: '1/2' => (1 / 2)
Number readFromString: '(1/2)' => 0
Number readFromString: '1/2' => 1
Fraction readFromString: '(1/2)' => 0
Fraction readFromString: '1/2' => 1
Georg
Georg Heeg eK, Dortmund und Köthen, HR Dortmund A 12812
Wallstraße 22, 06366 Köthen
Tel. +49-3496-214328, Fax +49-3496-214712
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Von: [hidden email] [[hidden email]] Im Auftrag
von Vincent Lesbros
Gesendet: Dienstag, 19. März 2013 11:38
An: [hidden email]
Betreff: [vwnc] Fraction is not a Number ?
Hi,
Why '(1 / 2)' asNumber => 0 ?
while (1 / 2) printString => '(1 / 2)'
What is the standard way to convert numbers from string and reverse ?
I Thought it was with printString and asNumber but it doesn't work.
Vincent
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