> 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 <[hidden email]> 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
>
>
>