An object key shouldn't need to be declared before an assignment that specifies it.

[fernandortdias]

Feature request

Input Code

a.b.c.d = 10 
alert("a.b.c.d = " + a.b.c.d)

Expected Behavior

a.b.c.d = 10

Current Behavior

error;

Possible Solution

var a;

if (typeof a === "undefined" || a === null) {
a = {};
}

if (a['b'] == null) {
a['b'] = {};
}

if (a['b']['c'] == null) {
a['b']['c'] = {};
}

if (a['b']['c']['d'] == null) {
a['b']['c']['d'] = {};
}

a.b.c.d = 10;

alert("a.b.c.d = " + a.b.c.d);

Context

As Coffeescript doesn't require variables do be declared before assigning values to them, I'd expect that a missing key in a object hadn't to be declared either before an assignment to that key. This way it would be much easier to represent a sparse matrices as objects.

I've got the "possible solution" above using this code in CoffeeScript:

a = {} unless a?
a['b'] = {} unless a['b']?
a['b']['c'] = {} unless a['b']['c']?
a['b']['c']['d'] = {} unless a['b']['c']['d']?

a.b.c.d = 10

alert("a.b.c.d = " + a.b.c.d)

Environment

• CoffeeScript version: 2.5.1
• Node.js version: N/A

[edemaine]

The canonical solution to this is

a ?= {}
a.b ?= {}
a.b.c ?= {}
a.b.c.d = 10

Are you suggesting that a.b = 5 should automatically prepend a ?= {}? This seems likely dangerous and bad, as it's using JavaScript notation with a very non-JavaScript meaning.

I could imagine a different operator like a!.b = 5 (or some other notation) that automatically does a ?= {} before a.b = 5, though.

[vendethiel]

Duplicate of #2610, #1870, #1642, #1394, and somewhat #1141 & #881.