Add "safe navigation"/existential operator about sdk HOT 21 CLOSED

Dart has had ?. and ?? for several years now. It's closed because it's done. :)

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This comment was originally written by [email protected]

This was entered as a Defect in error, please change to Enhancement.

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This comment was originally written by [email protected]

Removed Type-Defect label.
Added Type-Enhancement label.

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This comment was originally written by [email protected]

Added Area-Language, Triaged labels.

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Interesting idea. We'll think about it.

Set owner to @gbracha.

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Issue #66 has been merged into this issue.

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This comment was originally written by [email protected]

A replacement of || for null-checks would also be quite useful, as || now works only on booleans. C# uses ?? for this purpose.

foo = mightBeNull || default; //in JS

becomes

foo = mightBeNull ?? default; //in C# or hopefully future Dart?

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This comment was originally written by [email protected]

+1 Dart really needs to copy CoffeeScript's existential as this is one of the biggest friction points I'm facing (moving from CoffeeScript).

Both these snippets are obvious, more readable, require less boilerplate and make it effortless to write safer code:

zip = lottery.drawWinner?().address?.zipcode;
foo = mightBeNull ?? default;

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Added apr30-triage label.

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Removed apr30-triage label.

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Added triage1 label.

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Added this to the Later milestone.
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This comment was originally written by [email protected]

∃ and ∄ would be appropriate to use for this. As our current static keyboard layouts fail to provide a usable input mechanism for such symbols, an ascii alias might be usefull ;)

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Issue #5630 has been merged into this issue.

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This comment was originally written by [email protected]

How about making this more like as in Objective C where you can send messages to NIL that then will be ignored?

In case of chaining multiple messages send to a given object and objects returned thereof, each message sent to a NIL objects would return a NIL again so that the chained calls would not fail.

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This comment was originally written by [email protected]

I like Obj-C approach as well but for ease of determining the source of errors, it may be a good idea to be explicit when it doesn't matter.

The existential operator is a convenient choice to opt-in for this.

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This comment was originally written by [email protected]

I use in Javascript when recibe info in Json files with optative fields.

((student.preferences || {}).hobies || {}).bricollage

I prefer any sugar sintax not LISP (ie: without the intrusive parenthesis).

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This comment was originally written by [email protected]

For the ease of discussion, I'll add that the ?? operator in C# is called the null-coalescing operator.

Here's an example I've used in C# where this operator has come in handy:

if ((stringMightBeNull ?? "").Length == 0) {
    // string is empty or null
}

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I miss this from Ruby, fwiw.

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Met with external customers today, and they asked for this, or something like it. They'd be fine with C#'s null-coalescing operator.

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What happened to this? Why is it closed?

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