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Allow multiple parameters for the [] and []= operators. #8980

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lrhn opened this issue Mar 7, 2013 · 4 comments
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Allow multiple parameters for the [] and []= operators. #8980

lrhn opened this issue Mar 7, 2013 · 4 comments
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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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@lrhn
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lrhn commented Mar 7, 2013 •
edited

We could allow multiple parameters on the [] and []= operators, e.g.,

class Matrix2D<V> {
  V operator[](int x, int y);
  void operator[]=(V value, int x, int y);
}

That would allow multi-dimensional lookups and assignments with a good-looking syntax. Usage would be the expected:

matrix[2,4] = matrix[1,3] + 1;

Using the wrong number of parameters for an object would be a noSuchMethod call, just as for a similar methods.

The alternative is to write "get" and "set" methods, which isn't as readable.

The necessary grammar changes is to allow the same arguments between [] as between () in a call, and relax the requirements on arguments for operator[] and operator[]=.
I put the value of operator[] first, so that it's possible to use named parameters, e.g. foo[x:42, y:12] = 10.

We can also disallow optional parameters to begin with.

(This was not my idea, but I liked it when I heard it!)
@munificent
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I remember discussing this with Gilad a long time ago, but I guess I never filed a bug. Given that the "() operator" (i.e. "call") allows arbitrary method signatures, it seems inconsistent that [] does not. It's certainly a painful limitation when you want to define any kind of matrix or multi-dimensional array type (see: every game ever written).

I would really really like this feature.

@gbracha
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gbracha commented Aug 25, 2014

FTR: There is no () operator, and therefore no inconsistency. You want to introduce an inconsistency by making certain operators special as a syntactic sugar. Maybe someday, but not very soon.

Set owner to @gbracha.
Added Accepted label.

@lrhn
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lrhn commented Dec 4, 2014 •
edited

The current request doesn't require varargs - it just treats everything between '[' and ']' as arguments to operator[], just as if you had written '(' and ')' to specify arguments to call.

It will work fine for two-dimensional matrices (operator[](x,y)) but not for arbitrary-dimension matrices implemented in one class.

@lrhn lrhn added Type-Enhancement area-language Dart language related items (some items might be better tracked at github.com/dart-lang/language). labels Dec 4, 2014
@kevmoo kevmoo added P2 A bug or feature request we're likely to work on type-enhancement A request for a change that isn't a bug and removed accepted labels Feb 29, 2016
@lrhn lrhn removed the P2 A bug or feature request we're likely to work on label Aug 31, 2020
@lrhn lrhn mentioned this issue Sep 30, 2022
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@munificent munificent added the closed-duplicate Closed in favor of an existing report label Sep 30, 2022
@munificent
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Closing as duplicate of dart-lang/language#2534.

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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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