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Re^4: Strong typing and Type Safety.A multilanguage approach

by nikosv (Hermit)
on Nov 20, 2010 at 08:23 UTC ( #872653=note: print w/ replies, xml ) Need Help??


in reply to Re^3: Strong typing and Type Safety.A multilanguage approach
in thread Strong typing and Type Safety.A multilanguage approach

that using the numeric + operator on a Perl string is "implicit" and therefore weakly typed

no but the conversion from string to number is


Comment on Re^4: Strong typing and Type Safety.A multilanguage approach
Re^5: Strong typing and Type Safety.A multilanguage approach
by eyepopslikeamosquito (Canon) on Nov 20, 2010 at 10:47 UTC

    No. By using the + operator, you are explicitly asking for the string to be converted to a number. Why do you say it is implicit? (This thread may be heading towards Room 12A).

      Quoting Modern Perl Books page 15

      Perl will do its best to coerce values to the proper type (see Coercion, page 47), depending on the operators you use. Be sure to use the proper operator for the type of context you want.

      Quoting Wikipedia

      Type Conversion In most languages, the word coercion is used to denote an implicit conversion, either during compilation or during run time.

        Allow me to assure you that the author of Modern Perl disagrees with your interpretation of his words.

      Sure, I can "explicitly" do 0+ with the intent of converting a string into a number. "Explicit" describes my motivation. But, no, 1+$duration is not an explicit type conversion, it is explicit addition that implies a type conversion, if required.

      I can write 1+$duration with no intention of doing a conversion. If I am mistaken in thinking that $duration holds a numeric value and write 1+$duration, since the explicit request for addition includes in it an implicit possibility of type conversion, the compiler can't tell that I didn't mean for a conversion to happen. The type conversion is called "implicit". Having to write 1+(int)$duration is much more explicit. Type conversion is only done when I explicitly say "do a type conversion" not when I say "do addition" and can't separately specify that I want a conversion.

      - tye        

        1+$duration is not an explicit type conversion, it is explicit addition that implies a type conversion, if required.

        + is a monomorphic operator. So is .. Perl values are polymorphic.

        Arguing that operator-enforced coercions in Perl are implicit is silly nonsense; to do so you must assume a priori that values should be monomorphic.

        I can write 1+$duration with no intention of doing a conversion.

        You can also write $string + $duration with no intention of performing addition, but that has nothing to do with typing and everything to do with you writing buggy (or poorly understood) code.

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