comment on

My practices are these.

I always make sure that it would be clear from the error message that it's an error. I don't use a single prefix, just include one some word like qw"error cannot failed failure". It can be very confusing if you write

read $FOO, $s, $l or do {
    warn "reading foo file";
    last PROCESS_FOO;
}
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because it will seem to be a status message saying the program is starting to read the foo file.

I always include $! if its value is meaningful (that is, if the function that fails sets it).

I always provide the implicit line number (although I almost always ignore it when I read the error message). The exception is some status messages that are not errors.

I don't capitalize the error message.

I sometimes give details about the error, sometimes not. I add the details in the die statement if the error actually happens and I don't understand why.

If you want to know more about my style, here is the complete (ok, I could have missed some) list of error statements in two of my programs.

        1 < ($scope = 0 + $scope) or
                die "nearword scope must be greater than 1";

        open $file, "<", $filename or
                die "cannot open text file for nearword: $!";

                $nl <= $n && $n <= $nle or
                        die "postcondition failed";

                @a or
                        die "internal error: quantile1 called on empty
+ list, n=" . $n;

                        @{$hheap[1]} and # DEBUG
                                die "internal error: couldn't pop non-
+empty hheap";

                $used{$q}++ and
                        warn "single-link internal: used hash corrupt"
+;

        @order == @point && @gap == @order or
                die "singlelink internal error: lost or duplicate elem
+ents: order " . @order . ", point " . @point . ", gap " . @gap;

        keys(%$hash) == @$heap or
                die "assertion failed: hheap size mismatch: hash " . k
+eys(%$hash) . ", heap " . @$heap;
        for $k (0 .. @$heap - 1) {
                ref($$heap[$k]) eq "ARRAY" or
                        die "assertion failed: non-array heap element 
+index " .
$k;
                exists($$hash{${$$heap[$k]}[1]}) or
                        warn("assertion failed: hheap element missing 
+from hash: "), die "index " . $k . ", element " . ${$$heap[$k]}[1] . 
+", distance " . ${$$heap[$k]}[0];
                $k == $$hash{${$$heap[$k]}[1]} or
                        warn("assertion failed: hheap index mismatch: 
+"), die "
   real index " . $k . ", element " . ${$$heap[$k]}[1] . ", hash value
+ " . $$hash{${$$heap[$k]}[1]};

                ${$$heap[($k - 1) >> 1]}[0] <= ${$$heap[$k]}[0] or
                        warn("assertion failed: hheap heap mismatch: "
+), die "parent index " . $k . ", element " . ${$$heap[$k]}[1] . ", di
+stance " . ${$$heap[$k]}[0] .
                                ", child index " . (($k - 1) >> 1) . "
+, element
" . ${$$heap[($k - 1) >> 1]}[1] . ", distance " . ${$$heap[($k - 1) >>
+ 1]}[0];

        1 == @ARGV or
                die "Usage: rock-cut -g goal hierarchy.xml";

                length($id) or
                        die "invalid input: element with no id";
                exists($element{$id}) and
                        die qq[invalid input: duplicate element id "$i
+d"];

                length($id) or
                        die "invalid input: cluster without id";
                exists($cluster{$id}) and
                        die qq[invalid input: duplicate cluster id "$i
+d"];

        @root or
                die(@root ? "error: no root clusters found -- wierd" :
+ "error: no clusters found at all");

                exists($$d{"weight"}) and do {
                        if (defined($$d{"weight"}))
                                { warn qq[warning: cluster included in
+ more than one cluster: "$n"]; }
                        else
                                { die qq[error: circular clusters: "$n
+"]; }
                };

                                { warn qq[cluster "$c" has non-existen
+t child "$cd"]; next; };

                defined($mi) or do {
                        warn "clusters fragmented totally, decrease go
+al or outlier_max";
                        last;
                };
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In reply to Re: Style guide for error messages? by ambrus
in thread Style guide for error messages? by xdg

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