Literal symbols are not accepted as const map keys.

[DartBot]

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

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What steps will reproduce the problem?

class A {}
class B {}

main() {
  var map = const <Symbol, int>{#A:0, #B:1};
  print(map);
}

the Editor shows this warning 'Keys in a map cannot be equal'
and running the code produces the error: 'key value must not implement operator =='.

The same behavior occurs with var map = const <Symbol, int>{const Symbol('A'):0, const Symbol('B'):1}

It works removing the const keyword but the DartEditor still shows the warning.

What version of the product are you using? On what operating system?

Editor: 1.0.1_r30657 (2013-11-25)
OS: Mac OS X - x86_64 (10.9)

[peter-ahe-google]

Added Area-Analyzer, Triaged labels.

[peter-ahe-google]

Two bugs here: an analyzer bug, and a VM bug.

I've dedicated this bug to the analyzer and the corresponding VM bug is issue #15445.

[DartBot]

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

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Same warning with class literals.

class A {}
class B {}
main() {
  var map = const <Type, int>{A:0, B:1};
  print(map);
}

[bwilkerson]

Added this to the 1.1 milestone.
Removed Priority-Unassigned label.
Added Priority-Medium label.

[lrhn]

Class literals (Type objects) suffer from the same problem as symbols: They override the operator== method of Object, so they are not allowed as const map keys.

They override equals because we didn't want to canonicalize the potentially infinite number of Type objects that a program can create due to risk of memory leaking, but we still want the Type objects to be equal if they represent the same Type.

[yjbanov]

Duplicate? See: #­13245

[bwilkerson]

https://codereview.chromium.org/113143004/ (bleeding edge revision 31303)

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Set owner to @bwilkerson.
Added Fixed label.

[lrhn]

If "fixed" means not giving a warning, then it's a bug.
The symbol constant objects still implement operator==, so they are not allowed in a switch case or const map literal. The analyzer doesn't warn, but the code still doesn't run in the VM.

See: https://groups.google.com/a/dartlang.org/forum/?fromgroups#!topic/misc/TPe9-SfDRps

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Added Triaged label.

[bwilkerson]

Removed this from the 1.1 milestone.
Added this to the 1.3 milestone.

[bwilkerson]

"The static type of a symbol literal is Symbol."
"If d is a class, type alias or type parameter the static type of e is Type."

Neither dart:core::Symbol nor dart:core::Type implements nor inherits an implementation of == other than the one in Object. (They are both abstract classes with no explicit superclass, mixins, or interfaces.)

Therefore, based on the static type information, I don't believe that there is suppose to be an error here. The analyzer cannot be expected to use the run-time type of a literal when it isn't given in the specification. Please let me know if my reasoning is faulty.

(I would almost argue that it's a bug in the VM that the internal Symbol defines ==, but user code can have the same problem too. Perhaps we should define == on dart:core::Symbol in order to make it possible to catch this problem in the analyzer.)

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Added Fixed label.