Support computed properties in `Json`, `Map` literals

[Chriscbr]

Use Case

If you are initializing a new Map or Json object and one if its keys is a variable (not a fixed string), then it's not easy to accomplish today. One way to do it is to create a MutJson object, set an item, and then if want it to be immutable, to use Json.deepCopy, but it's awkward and is inefficient because of the copying involved:

let key = "name";
let x = MutJson {};
x[key] = "wingy";
let y = Json.deepCopy(x);

Proposed Solution

Support computed properties, similar to JavaScript: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#computed_property_names

In Wing this might look like:

let key = "name";
let x = Json {
  [key]: "wingy"
};

---

An alternative design could be to change Wing's object literal syntax so keys that aren't surrounded by quotes have to refer to variables:

let x = Json {
  key: "wingy" // error: no variable named "key" is defined
};

let key = "name";
let y = Json {
  key: "wingy" // ok
};

But since Wing interoperates with TypeScript, I suspect this would confuse folks and add friction for people switching to Wing, so I recommend against it.

Implementation Notes

No response

Component

Language Design, Compiler

Community Notes

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[boyney123]

Personally coming from TS/JS background I prefer this, FWIT

let key = "name";
let x = Json {
  [key]: "wingy"
};