Maybe this is a naive question, but can you just split the task into the following two?
1. Check whether whether the string is syntactically an ISBN number. This can be done, e.g., using a regex. 2. Check the the check character. Calculate the check character from the (now to be known) syntactically valid string. ISBNValidator>>isValidISBN: aString ^(self isSyntacticallyValid: aString) and: [self isCheckCharacterValid: aString] Kind regards, Steffen Am .09.2020, 07:35 Uhr, schrieb Roelof Wobben via Pharo-users <pharo-users@lists.pharo.org>:
Nope, with your idea I cannot make this part work : he ISBN-10 format is 9 digits (0 to 9) plus one check character (either a digit or an X only). In the case the check character is an X, this represents the value '10'. These may be communicated with or without hyphens, and can be checked for their validity by the following formula: (x1 * 10 + x2 * 9 + x3 * 8 + x4 * 7 + x5 * 6 + x6 * 5 + x7 * 4 + x8 * 3 + x9 * 2 + so I mean the calculation. Roelof Op 4-9-2020 om 06:45 schreef Roelof Wobben: oke, then I could use your idea but then I have to make the code for calculating if its a valid number. and I wonder if the code will not be too big. I learned that it is good that a method does only 1 thing and this one seems to be doing more then 1 thing. Roelof Op 4-9-2020 om 05:24 schreef Richard O'Keefe: What part of "return false if there are not exactly 10 characters left after discarding dashes" fails to handle the empty string? A test case for the empty string is is only valuable if the empty string is NOT a special case. On Wed, 2 Sep 2020 at 22:52, Roelof Wobben <r.wob...@home.nl> wrote: Op 2-9-2020 om 12:38 schreef Richard O'Keefe: There is simply no point in "taking the first nine numbers out". And there shouldn't BE a test for the string being empty, anywhere. '' '-' '---' and so on should all be handled the same way. Oh well, what stops you doing digits := aString select: [:each | each ~= $-]. digits size = 10 ifFalse: [^false]. lastDigit := digits la ost. digits := digits copyFrom: 1 to: 9. ( (lastDigit = $X or: [lastDigit isDigit]) and: [ digits allSatisfy: #isDigit] ) ifFalse: [^false]. Now my code does not do this, but it is just 16 lines of code with nothing that it would make sense to extract. Nothing only that I could not think of this one for myself. If I do it the TDD way I come more on the way Im currently thinking but does this case then be covered test14_EmptyIsbn | result | result := isbnVerifierCalculator isValidIsbn: ''. self assert: result equals: false and still I have to do the calcualation to see if it's valid. If I understand the code well I can use the digits variable ? Roelof
