make dealing with null less painful

[trinarytree]

problem 1: fallback values.
suppose you have a sequence of fallback values to use when you encounter null.
python example: v = x or y or z
js example: v = x || y || z;
dart example:
v = x != null ? x :
    y != null ? y :
    z;
yuk. notice how x and y are both repeated.
if x is a complex expression, perhaps an expression you aren't willing to evaluate twice, it gets even uglier:
v = complexExpressionX;
if (v == null) {
  v = complexExpressionY;
}
if (v == null) {
  v = complexExpressionZ;
}

and if v is a setter, perhaps something you don't want to call twice, it can get even uglier:
var tempV;
v = complexExpressionX;
if (v == null) {
  v = complexExpressionY;
}
if (v == null) {
  v = complexExpressionZ;
}
v = tempV;

and if this is inside an expression, where you can't have separate statements, e.g.
when trying to set a final value in a constructor, you need to get even uglier, e.g. by
creating a static method.

problem 2: navigating an object graph.
suppose you want to navigate down an object graph but just want null if any part is null.
groovy example: x?.y?.z
dart example:
x != null && x.y != null ? x.y.z : null;
and if the getters are expensive...
var tempZ;
var tempX = x;
if (tempX != null) {
  var tempY = tempX.y;
  if (tempY != null) {
    tempZ = tempY.z;
  }
}
and if this is inside an expression, where you can't have separate statements, it gets uglier.
e.g. you may need to extract a function. yuk.

groovy has null-coalescing and safe navigation operators: ?: and ?.
can dart get something like these to avoid the above pain?

[DartBot]

This comment was originally written by @zoechi

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see also

• http://dartbug.com/22
• http://dartbug.com/41
• http://dartbug.com/8598

[DartBot]

This comment was originally written by @seaneagan

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for "problem 1: fallback values" see issue #1236

[kasperl]

Added Area-Language, Triaged labels.

[gbracha]

This bug covers multiple requests, that are covered by several other bugs. I'm closing it asa duplicate. I have to pick one issue as a dup, I'll use 41.

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Added Duplicate label.
Marked as being merged into #41.