Checked exceptions

[Thomas May]

Reading over the current draft proposal, I'm not sure I see how that might work.

Would there be some sort of match operator that you could override?  Such as,

String num = "1.23";
if (new Pattern("#.##").convert(num) double val) {
  print("Hi " + val);
}

If that's the case, what would convert return?  Maybe something like

DoubleMatch

or

Match<T>

(like IntStream, or DoubleStream).

If that is the case, then it would be possible to extend the API in useful ways.  We could make something like

Match<T> XmlParser.convert(InputStream i, Class<T> type)

and then use it like

if (XmlParser.convert(i, Foo.class) Foo bar) {

}

Am I way off base here or are you thinking of something better?
________________________________
From: Brian Goetz <brian.goetz at oracle.com>
Sent: Thursday, October 17, 2019 10:17 AM
To: Thomas May <tmay at clearwateranalytics.com>; jdk-dev at openjdk.java.net <jdk-dev at openjdk.java.net>
Subject: Re: Checked exceptions

CAUTION: External Email


> The example that comes to mind is Double#parseDouble.  It's annoying to have to deal with NumberFormatException, the API would jive better if instead it returned an Optional<Double>.  But I realize that isn't possible without a lot of breakage, so what about instead a optionalParseDouble that returns a Optional<Double>?
>

Stepping back from the exceptions question for a minute, the way I would
prefer to address problems like this is via pattern matching. If we
expose a pattern whose target is a string, and which produces a binding
variable of type double if the string is the string representation of a
double, then either the pattern matches and produces a valid double, or
it doesn't match.  The advantage of this over the Optional approach is
that is nestable with other patterns, so if we have a pattern that
produces a String, we can compose it (via nesting) with the
double-parsing pattern.

Once we have pattern matching, it will make sense to expose all sorts of
parsing patterns, which work similarly to the Optional-bearing version
of your method, but compose better.



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