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Postings from June 2022
> On Jun 8, 2022, at 07:12, Paul LeoNerd Evans <leonerd@leonerd.org.uk> wrote:
>
> use builtin 'blessed';
>
> try {
> maybe_call_a_func();
> }
> catch ($e) {
> if(blessed $e) {
> warn "Caught a user-defined exception of type " . (blessed $e);
> }
> else {
> warn "Caught a plain stringy exception";
> }
> }
>
> What should we do here?
>
> 1) Throw objects of some core-defined type, so `ref` and `blessed` are
> now true on these things, meaning they can be distinguished -
> including by some sort of `isa` test as might someday be added to
> `catch`, but thus breaking all existing code which inspects $@ or
> $e.
Worth clarifying: this won’t “break all existing code which inspects $@ or $e”; it would only break code that expects exception objects to be user-thrown errors.
(I know, of course, that you know that, but IMO it’s worth being specific about the scope.)
FWIW, I’ve never written such code. Whenever I care about an error object’s blessed-ness, I check its class. So I’d write, e.g.:
-----
try {
throw_object();
}
catch ($e isa Some::TLS::X::Base) {
# It’s a TLS-level error
}
catch ($e isa IO::Socket::X::Base) {
# It’s a socket-level error
}
catch ($e) {
warn "Some unhandled error: $e";
}
-----
I can’t speak for what others may have written, of course.
> 2) Throw plain strings that have some other, new way to query some
> hidden "error type" information stored within them. Maybe lets
> invent some new `builtin` funcs and imagine a hypothetical future
>
> use builtin 'extype';
>
> ...
> catch($e) {
> my $t = extype $e;
> if($t eq "SOMETHING") { ... }
> elsif ...
> }
Attaching metadata to plain scalars could be powerful. It feels like it would encourage “weirdness”, but I haven’t researched it. I know decorator-type things are a common feature in other languages.
-FG
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