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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.


  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?

  2. Arron: yes, you can. But you are discouraged from doing that by the style guide, see


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