On Monday, 25 February 2013 at 20:21:55 UTC, Vladimir Panteleev
wrote:
On Monday, 25 February 2013 at 20:09:14 UTC, Lars T.
Kyllingstad wrote:
Exceptions are designed to handle exceptional cases. A
missing environment variable isn't exceptional, it is
commonplace.
I disagree. I don't know your uses cases, but as far as I can
see, if the program expects the variable to be present in the
environment, then it is no different from a missing file which
the program expects to be present, or malformed user input.
That would depend on the application.
Could you provide a specific example? It's difficult to discuss
the merits of either approach without some use cases.
Well, take Phobos, for instance. Besides std.process, there are
two places where environment/getenv is used: std.file.tempDir()
(POSIX version) and std.path.expandTilde(). None of them throw
if the variables in question don't exist, they both take some
default action instead.
As I see, there are two major cases:
1) The program expects a variable to be set. An example of this
is COMSPEC / SHELL. These variables ought to be set on any
system, so the user is not expected to verify this himself. The
variables not being set is an exceptional sitation.
2) A variable may or may not be set, such as the case of
passing additional options via the environment (such as
INCLUDE, or LD_PRELOAD). The program will take specific action
if the variable is not set, such as pretending it is empty, or
defaulting to some other setting like one in a configuration
file.
It seems like your approach caters to the second situation
exclusively. I've mentioned the problems of applying this
approach to the first situation in my previous post.
What if the variable is set, but empty? Is that very different
from the situation where it doesn't exist at all? In my opinion,
when it comes to environment variables, no.
You mention 'rm -rf $FOO/$BAR' as a "classic catastrophic bug" in
shell scripts. This is just as much a problem if FOO and BAR are
simply empty, and throwing from opIndex() won't help you with
that. You still have to test for empty(), which would *also*
test for null.
Lars
