casting a null value throws a NullPointerException

[DartBot]

This issue was originally filed by [email protected]

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Per the spec on casts[1], the following code throws NullPointerException:

  var x = null;
  String s = x as String;

as does this following (type-correct) code:

  String x = null;
  String s = x as String;

This is surprising to me - null is a legal value for the String type.
It's also different to how e.g. Java and C# behave.

I can see use cases for asserting non-nullity, but this is orthogonal to casting (unless non-nullable types are added, see issue #22).

One counterargument is that the specified behaviour is consistent with 'is'.
I'm used to that inconsistency from Java (spelling it instanceof reduces the confusion there) so I'm not sure how confusing it is.

[1] http://www.dartlang.org/docs/spec/latest/dart-language-specification.html#h.4pppxtxtu3v2

[dgrove]

Set owner to @gbracha.
Added Area-Language, Triaged labels.

[DartBot]

This comment was originally written by @tomaszkubacki

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Dart shouldn't go too far from what's natural for java/c# devs

[gbracha]

Corrected in 0.11 draft.

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Added this to the M1 milestone.
Added Done label.