Skip to main content

New try/catch syntax ready to use

Posted by Kasper Lund


We're very close to being able to turn off the support for the old
try-catch syntax. Early next week attempts to use the old syntax will
lead to compile-time errors. The new syntax already works today so now
would be a fantastic time to update your code.

The old syntax like:

   try { ... } catch (var e) { ... }
   try { ... } catch (final e) { ... }
   try { ... } catch (T e) { ... }
   try { ... } catch (final T e) { ... }

translates to new syntax like this:

   try { ... } catch (e) { ... }
   try { ... } catch (e) { ... }
   try { ... } on T catch (e) { ... }
   try { ... } on T catch (e) { ... }


and the local variable introduced to hold the reference to the caught
exception (e) is implicitly final in all cases.

Why did we make this change? The M1 Updates article explains it best.

Comments

  1. From M1 Update:

    "This causes some confusion and some nasty syntactic corner cases. For example, if you just have catch(foo) does that mean “catch an exception of any type and bind it to foo” (which lines up with other parameters in Dart where the type annotation is optional), or does it mean “catch an exception of type foo and don’t bind it to a variable” (which is what it would mean in Java)?"

    Does this mean you can have classes that start with a lowercase letter?

    ReplyDelete
  2. Arron: yes, you can. But you are discouraged from doing that by the style guide, see http://www.dartlang.org/articles/style-guide/#do-name-types-using-uppercamelcase.

    ReplyDelete

Post a Comment

Popular posts from this blog

Const, Static, Final, Oh my!

Posted by Seth Ladd

(This is an "oldie but a goodie" misc@dartlang.org post originally written by Bob Nystrom. It is being posted here as the explanations still ring true.)

Bob writes:


"static", "final", and "const" mean entirely distinct things in Dart:

"static" means a member is available on the class itself instead of on instances of the class. That's all it means, and it isn't used for anything else. static modifies *members*.

"final" means single-assignment: a final variable or field *must* have an initializer. Once assigned a value, a final variable's value cannot be changed. final modifies *variables*.

"const" has a meaning that's a bit more complex and subtle in Dart. const modifies *values*. You can use it when creating collections, like const [1, 2, 3], and when constructing objects (instead of new) like const Point(2, 3). Here, const means that the object's entire deep state can be determ…

The new AdWords UI uses Dart — we asked why

Google just announced a re-designed AdWords experience. In case you’re not familiar with AdWords: businesses use it to advertise on google.com and partner websites. Advertising makes up majority of Google’s revenue, so when Google decides to completely redo the customer-facing front end to it, it’s a big deal. The Dart team is proud to say that this new front end is built with Dart and Angular 2. Whenever you asked us whether Google is ‘even using Dart for anything,’ this is what we had in mind but couldn’t say aloud. Until now. We asked Joshy Joseph, the primary technical lead on the project, some questions. Joshy is focusing on things like infrastructure, application latency and development velocity, so he’s the right person to ask about Dart.Q: What exactly did we launch on Monday?It’s a complete redesign of the AdWords customer experience that is rolling out slowly as a test to a small initial set of advertisers. The most noticeable thing is probably the Material Design look and f…

Dart 1.12 Released, with Null-Aware Operators and more

Dart 1.12.0 is now released! It contains the new null-aware operators language feature, and enhancements to pub, Observatory, dartdoc, and much more.

Null-aware operators

The new null-aware operators help you reduce the amount of code required to work with references that are potentially null. This feature is a collection of syntactic sugar for traversing (potentially null) object calls, conditionally setting a variable, and evaluating two (potentially null) expressions.

Click or tap the red Run button below to see them in action.

??

  if null operator. `expr1 ?? expr2` evaluates to `expr1` if not `null`, otherwise `expr2`.


??=

  null-aware assignment. `v ??= expr` causes `v` to be assigned `expr` only if `v` is `null`.

x?.p

  null-aware access. `x?.p` evaluates to `x.p` if `x` is not `null`, otherwise evaluates to `null`.

x?.m()

  null-aware method invocation. `x?.m()` invokes `m` only if `x` is not `null`.

Learn more about Dart's null-aware operators in our Language Tour.

.packages fi…