Propose enhancement of field initializers

[DartBot]

This issue was originally filed by prujoh...@gmail.com

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Propose that this:

class Foo{
final myOtherClass;

Foo()
: myOtherClass = new myOtherClass()

}

also allow this:

class Foo{
final myOtherClass = new myOtherClass();

Foo();
}

See: https://groups.google.com/a/dartlang.org/group/misc/browse_thread/thread/32998e270e3cb57b/ec5cfe02c5acfee5#ec5cfe02c5acfee5

[munificent]

More specifically, I believe John's proposal is to allow non-constant initializer expressions for final non-static fields. Java and C# allow this and, as far as I know, it doesn't have any of the hairy implications that static initializations have. It's basically syntactic sugar for running an initializer expression at the beginning of the constructor body.

[DartBot]

This comment was originally written by prujohn...@gmail.com

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Yes. Thanks for putting a finer point on it. :)

[jtmcdole]

Added Area-Language, Triaged labels.

[jtmcdole]

Set owner to @gbracha.

[gbracha]

Added Accepted label.

[gbracha]

We are looking at changes to initialization.

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Removed Type-Defect label.
Added Type-Enhancement label.

[DartBot]

This comment was originally written by pr...@gmail.com

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Glad to see this is v.08. Thanks!

[gbracha]

Don't thank us yet!

a. The change only applies to static variables. We're still thinking about the implications for instance variables. That's a lot harder.

b. As the spec notes, the changes aren't implemented yet. But they will be.

And thank you for bearing with us.

[DartBot]

This comment was originally written by prujohn...@gmail.com

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Excellent progress though. I still applaud it.

[anders-sandholm]

Always executed before any expression in the constructors' initializer list. 'this' must not be in scope for the expression. In addition, this prevents setting the final field in any other part of the code.

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Added this to the M1 milestone.

[gbracha]

Spec version 0.11 allows arbitrary code in an instance initializer, provided "this" is not used.

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Added Done label.

[DartBot]

This comment was originally written by pr...@gmail.com

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Excellent!

[DartBot]

This comment was originally written by @seaneagan

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in the following:

var c = 'c';

class A {
  var c = 'd';
  var b = c;
}

main() => print(new A().b);

I assume it will print 'c', but it could be surprising since normally instance variables can be accessed without "this." in class bodies.

[DartBot]

This comment was originally written by ladicek@gmail.com

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Sean: I think that your example will fail (compile-time error?), because in the initializer of 'b', you implicitly access 'this'. The access to 'c' in this initializer is actually an access to 'this.c', because the 'c' inside the class shadows outer 'c'.

I don't think that scoping rules are changed by this, and it would be really confusing if they were (as you note).

[gbracha]

Changed the title to: "Propose enhancement of field initializers".