Re: Exception Names

Eric Sosman <Eric.Sosman@sun.com> writes:


  When testing such properties before using them, there always
  is the slight chance that the properties might have changed in
  the meantime.

  Therefore, the operation to use the property must have a means
  to signal a failure. But this means does not have to be an
  exception, it also can be any other possible path of
  information transfer to a caller, like the value of the call
  expression.

  Now, often they say that exceptions should be used for
  ?exceptional situations?, but this might be a tautology. It
  does not actually explain, what constitutes an ?exceptional
  situation?.

  I just had the idea of another approach: The notation of calls
  of Methods in programming was derived from the notation of
  functions in mathematics?:

      y = sin x (1)

  . This means ?y is the sine of x.?. It makes sense even as a
  natural-language sentence: The order of the words in (1) is
  the same order as in the English-language sentence.?

  Therefore, one can consider a program with

      y = sin x

  as very readable.

      write( value, file ); (2)

  also can be nearly-parsed as natural language: ?Write the
  value to the file.?

  But when both value-methods and action-methods are mixed
  we get:

      status = write( value, file ); (3)

  . Now there is no natural-language English sentence anymore
  that makes sense, correctly describes what is intended by the
  above statement, and preserves the order of words (structure)
  of the above statement (3). Also, such usage is not known in
  mathematics.

  With exceptions, one can continue to use the more ?natural?
  forms of function/procedure call as in (1) and (2).:

    try
    { write( value, file ); }
    catch( final java.example.cantWriteToFileException e )
    { ... }

  Now, this, again, /can/ be nearly-read as a natural-language
  sentence: ?Try to write to value to the file, but if your
  attempt should fail, then ....?, the order of words is
  preserved.

  So a guide-line to use exceptions might then be:

      ?Use exceptions, when this makes your source code more
      readable. Especially, to give the call site a more
      natural-language-like structure.?

  ?: The Java Code Convention to always use verbs for method
  names are not followed by Sun Microsystems, Inc. itself:

      ?Methods should be verbs?

http://java.sun.com/docs/codeconv/html/CodeConventions.doc8.html#367

      ?static double sin(double a)?

http://download.java.net/jdk7/docs/api/java/lang/Math.html#sin(double)

  The correct guideline is given by Rob Pike:

      ?Procedure names should reflect what they do;
      function names should reflect what they return.?

http://www.lysator.liu.se/c/pikestyle.html

  For function names, this corresponds with the proven practice
  of mathematics. For both function names and procedure names,
  it corresponds with the structure of natural languages (at
  least, of English, the lingua-france of programmers). So it
  will make programs more readable.