Add a truthy operator

[Zectbumo]

Javascript and other languages have truthy tests that results in clean code:

  if (myStr);

Is it possible to have something reads better in Dart than any of the following:

  if (myStr != null && !myStr.isEmpty);

Even if we employed issue #41 and issue #1236 it gets worse:

  if (!(myStr?.isEmpty ?? true));

  if (!(myStr ?? '').isEmpty);

I wouldn't want to use any of those patterns. I would rather implement my own method:
http://pastebin.com/0bzDixFc

  if (isTruthy(myStr));

So, how about a truthy operator instead:

  if (!!myStr);

and maybe an abstract class to go along with it:

  abstract class Truthy {
    bool operator !!();
  }

Will Object implement Truthy?

[DartBot]

This comment was originally written by @zoechi

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Your examples can be simplyfied a bit (not shorter but IMHO easier to interpret)
 if (myStr != null && myStr.isNotEmpty);
 if ((myStr ?? '').isNotEmpty);
 if (myStr?.isNotEmpty ?? false));
 if ((myStr ?? '').isNotEmpty);

I think http://dartbug.com/22 is related too.
Having non-nullable types would take some burden off checking for truthiness.
I didn't like these truthy checks in JavaScript much. I prefer how in Dart one has to be more explicit. Being explicit could be simplified though.

  @­nonnull String myStr; // or whatever the syntax could be
  // all your examples would reduce to
  if (myStr.isNotEmpty)

[lrhn]

Added Area-Language, Triaged labels.

[gbracha]

Set owner to @gbracha.
Added WontFix label.