in reply to Re^5: When every microsecond counts: Parsing subroutine parameters
in thread When every microsecond counts: Parsing subroutine parameters

Named parameters means I don't have to pass a string of undefs because one particular call doesn't use those parameters.

I don't suppose you have any concrete examples you'd care to share?

APIs using positional parameters have a way of requiring difficult upgrade path.

And yet, other than tcl, I can't find reference to a single other language that has felt the need to implement named parameters?

Don't take me wrongly. The are absolutely some calls in many APIs (from many languages) that would benefit from this kind of self documentation.

  • CreateWindow() with its 11 parameters, some of which are themselves structs or bit-fileds is an obvious candidate.
  • CreateFile() with its 7 parameters including 4 bit-fields is another.

    But by and large, most of them are constructors. And where APIs regulary require the user to supply a list of undefs in order to use the call, architypically select undef,undef,undef, 0.1; these are generally and widely acknowledged, even by their authors, as being "ones that got away".

    With most functions that sometimes require more than 3 parameters, there is a 'natural ordering' that means that any omitted parameters will come at the end. Eg. substr, splice, read. Even in a function rich API like Perl's there are suprisingly few calls that require more than 3 args, and almost none that require the use of placeholders for distinct functionality.

    And that's the clue for me. If an API (beyond constructors), cannot be designed such that any omitted arguments fall at the end, then it is really two (or more) apis that have been conflated. select is the prime example as noted above, and it isn't hard to see how to change that:

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.

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    Re^7: When every microsecond counts: Parsing subroutine parameters
    by talexb (Chancellor) on May 18, 2008 at 20:18 UTC
        I don't suppose you have any concrete examples you'd care to share?

      Nope -- none to hand. That doesn't lessen my assertion that named parameters are a fine alternative to positional parameters, for the reasons I've already listed. I will modify that by saying that if there are just a few parameters to a function, positional parameters will work fine, but if there's a chance that some of the parameters might be optional, a hashref of named parameters is the way to go.

      Alex / talexb / Toronto

      "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

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        I will modify that by saying that if there are just a few parameters to a function, positional parameters will work fine, but if there's a chance that some of the parameters might be optional, a hashref of named parameters is the way to go.

        Then I think we are broadly in agreement. Then only areas left for arg negotiation are:

        1. How many parameters there need to be before using named parameters make sense.

          I'd set that to be: more than 4.

        2. The rarity with which the need arises (for non-constructors).

          On the basis of my not so exhaustive attempts to find counter examples, I'd say that the times when it's required purely because of the shear numbers of parameters, is really quite surprisingly rare.

          And, the occasions when it's needed to allow the ommision of placeholder undefs, is rarer still. Try as hard as I might, I find pretty impossible to come up with even a hypothetical good example of where there is no natural ordering that would allow logically optional parameters to be placed after all mandatory and more frequently required optional parameters.

          You need the situation where func( mandatory1, mandatory2, optional1, optional2 ) optional2 is logical when optional1 is not required, and optional1 is required when optional2 is not. I haven't found an example of that outside of conflations like select.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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          There's one in DBI that annoys me on occasion, and that's do($statement, \%attr, @bind_values);. In my code, I haven't found any use of that method where I needed to pass attributes, but I do have a fair number where I use bind values. Example: 
          $dbh->do('update some_table set some_column=?', undef, $some_string);

          [download]
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    Re^7: When every microsecond counts: Parsing subroutine parameters
    by educated_foo (Vicar) on May 19, 2008 at 01:47 UTC
      And yet, other than tcl, I can't find reference to a single other language that has felt the need to implement named parameters?
      I can think of Common Lisp, Ruby, and Python off the top of my head...
    		[reply]

        1. Ruby has to fake keyword args using a hash just like perl.
        2. Python has proper keywork args.

          I just never got into Python enough to reach the point where I would have noticed. (Seems it wasn't implemented until v2 anyway and thats probably after I last looked at it.)

        3. Lisp in all its many forms does my head in.

          I believe that keyword arguments are considered an extension. Still, that is implemented, so I defer.

          Just be really careful that you don't need to pass a value that looks like a keyword (eg:xxx), because things get really confusing really fast.

        So that makes 3. Four if you count Perl 6.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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          Just for the sake of completeness, we get to five if you count R, which allows one to intersperse positional and named parameters in a remarkably laissez-faire manner. It's not exactly a general-purpose language, though.
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          I believe that keyword arguments are considered an extension. Still, that is implemented, so I defer.
          Assuming you're talking about Common Lisp, keywords alone and keywords as argument specifiers are AFAIK both required parts of the spec, not just optional extensions. Other Lisp dialects can and do have different ideas - the only other relatively widely used Lisps, these days, are Scheme and Emacs Lisp (which both don't have keyword args).

          "What should it profit a man, if he should win a flame war, yet lose his cool?"
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