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Attention passengers: Flight 0703 is also known as Flight 451

  • Artigo

/>I hate
octal. Octal causes bugs. I hate bugs, particularly stupid "gotcha" bugs.

Foolish
C programmers do things like

int arr_flight
= 0703;

not
realizing that this does not assign the number 703, but rather 7 x 64 + 3 = 451.

Even
worse, foolish JScript programmers do things like

var arr_flight
= 0708;

var dep_flight
= 0707;

not
realizing that the former is a decimal literal but the latter is an octal
literal.

Yes,
in JScript it really is the case that if a literal begins with 0, consists of only
digits and contains an 8 or a 9 then it is decimal but if it contains no 8 or 9 then
it is octal! The first version of the JScript lexer did not implement those
rules, but eventually we changed it to be compatible with Netscape's implementation.

This
is in keeping with the design principle that I mentioned earlier, namely "Got a
problem? Muddle on through!" However, since this problem can be caught at
compile time, I think that the decision to make illegal octal literals into decimals
was a poor one.

It's
just a mess. Octal literals and escape sequences have been removed from the ECMAScript
specification, though of course they live on in actual implementations for backwards
compatibility.

This
is why I added code to JScript .NET so that any use of an integer decimal or octal
literal that begins with zero yields a compiler warning, with one exception.
Obviously x
= 0; does
not produce a warning!

Comments

  • Anonymous
    October 23, 2003
    Actually, not always the problem can be caught at compile time. If server generates pages with JS dynamically, the number containing 8 or 9 can appear in actual script once in a while. So the decision to correct the problem on the fly is not so bad as it seems.
  • Anonymous
    October 23, 2003
    Well, sure, but an ASP page could also generate a JScript block full of unterminated strings, and we catch those at compile time.
  • Anonymous
    October 24, 2003
    "This is why I added code to JScript .NET so that any use of an integer decimal or octal literal that begins with zero yields a compiler warning"Out of curiosity: How does the warning manifest itself? A callback to the script host? Or is JScript.NET not part of the whole Active Scripting family?
  • Anonymous
    October 24, 2003
    Correct -- JScript .NET does not participate in the old, 20th century unmanaged Windows Script interfaces. Rather, it uses the IVSA, aka "Script for the .NET Framework" interfaces. One of the shortcomings of the old Windows Script interfaces was that there was no way to surface warnings, only errors. IVSA provides a more fully-fledged compiler hosting mechanism.JScript .NET has some super-cool error recovery mechanisms for IVSA scenarios -- I might blog about them later, or convince Peter to.