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Change final to const for top-level and static variables now

Kasper Lund, engineer on the Dart project, sent a notice of a new breaking change to the Dart mailing list today.

Kasper writes:


TL;DR: Change final to const for top-level and static variables now.

Over the next days, we will stop treating references to top-level or
static final variables as compile time constant expressions. This
means that the following code will be illegal:

   final X = 42;
   final Y = const [ X ];

because you can only build constant lists out of compile time
constants. The fix is easy. Just replace final with const and you'll
be good to go (this works today):

   const X = 42;
   const Y = const [ X ];

The nice thing is that this paves the way for lazy static
initialization which allow you to initialize top-level and static
(final) variables with non-constant expressions like this:

   final Z = new Set<int>();

Note that this isn't supported across all our platforms just yet.

As always, you can join the discussion at the Dart mailing list, and ask questions at Stack Overflow.

Comments

  1. Just downloaded the Dart Editor 12440 and opened an "old" project. The error you'll get is "expression must be a compile-time constant". Changing final to const solved the issue.

    ReplyDelete

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