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Indexing into a constant list should be a constant expression. #8885

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munificent opened this issue Mar 2, 2013 · 2 comments
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Indexing into a constant list should be a constant expression. #8885

munificent opened this issue Mar 2, 2013 · 2 comments
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@gbracha
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area-language Dart language related items (some items might be better tracked at github.com/dart-lang/language). closed-duplicate Closed in favor of an existing report type-enhancement A request for a change that isn't a bug

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@munificent
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munificent commented Mar 2, 2013 •
edited

The minimal repro for the issue is:

const LIST = const ['a', 'b', 'c'];
const B = LIST[1]; // ERROR

Given that the list and the index are both constants, it seems reasonable that it should be a valid constant expression. But currently this gives an error.

I know I can (and will for now) rely on canonicalization to get around this, but it's particularly egregious in my real-world example:

class CompressionLevel {
  static const NONE     = CompressionLevel.LEVELS[0];
  static const FASTEST  = CompressionLevel.LEVELS[1];
  static const SMALLEST = CompressionLevel.LEVELS[9];
  static const DEFAULT  = CompressionLevel.LEVELS[6];

  static const LEVELS = const [
    //                       id  good lazy nice chain
    const CompressionLevel._( 0,  0,     0,   0,    0, _STORED),
    const CompressionLevel._( 1,  4,     4,   8,    4, _FAST),
    const CompressionLevel._( 2,  4,     5,  16,    8, _FAST),
    const CompressionLevel._( 3,  4,     6,  32,   32, _FAST),
    const CompressionLevel._( 5,  4,     4,  16,   16, _SLOW),
    const CompressionLevel._( 6,  8,    16,  32,   32, _SLOW),
    const CompressionLevel._( 7,  8,    16, 128,  128, _SLOW),
    const CompressionLevel._( 8,  8,    32, 128,  256, _SLOW),
    const CompressionLevel._( 9, 32,   128, 258, 1024, _SLOW),
    const CompressionLevel._(10, 32,   258, 258, 4096, _SLOW)
  ];

  final int _index;
  final int _goodLength;
  final int _maxLazy;
  final int _niceLength;
  final int _maxChain;
  final int _func;

  const CompressionLevel._(this._index, this._goodLength, this._maxLazy,
                           this._niceLength, this._maxChain, this._func);
}

Here, it would be tedious and error-prone to repeat all of the fields for NONE, FASTEST, SMALLEST, and DEFAULT.
@gbracha
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gbracha commented Mar 2, 2013

I have no problem with this. I do question whether we want to keep adding minor features at this time; thi seems like 2.0 thing to me.

Added Accepted label.

@gbracha
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gbracha commented Jan 3, 2015

Added Duplicate label.
Marked as being merged into #3059.

@munificent munificent added Type-Enhancement area-language Dart language related items (some items might be better tracked at github.com/dart-lang/language). closed-duplicate Closed in favor of an existing report labels Jan 3, 2015
@gbracha gbracha mentioned this issue Jun 3, 2015
Open
@kevmoo kevmoo added type-enhancement A request for a change that isn't a bug and removed type-enhancement labels Mar 1, 2016
@munificent munificent reopened this Dec 10, 2016
@munificent munificent mentioned this issue Dec 15, 2016
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area-language Dart language related items (some items might be better tracked at github.com/dart-lang/language). closed-duplicate Closed in favor of an existing report type-enhancement A request for a change that isn't a bug
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