Hi,
This would be covered by do expressions
<https://github.com/tc39/proposal-do-expressions>. You could just do:
```js
const category = do {
switch (...) {
...
};
};
```
On Sun, Feb 24, 2019 at 10:42 AM David Koblas <da...@koblas.com> wrote:
> After looking at a bunch of code in our system noted that there are many
> cases where our code base has a pattern similar to this:
>
> let category = data.category;
>
> if (category === undefined) {
> // Even if Tax is not enabled, we have defaults for incomeCode
> switch (session.merchant.settings.tax.incomeCode) {
> case TaxIncomeCode.RENTS_14:
> category = PaymentCategory.RENT;
> break;
> case TaxIncomeCode.INDEPENDENT_PERSONAL_SERVICE_17:
> category = PaymentCategory.SERVICES;
> break;
> case TaxIncomeCode.INDEPENDENT_PERSONAL_SERVICE_17:
> category = PaymentCategory.SERVICES;
> break;
> }
> }
>
> I also bumped into a block of go code that also implemented similar
> patterns, which really demonstrated to me that there while you could go
> crazy with triary nesting there should be a better way. Looked at the
> pattern matching proposal and while could possibly help looked like it
> was overkill for the typical use case that I'm seeing. The most relevant
> example I noted was switch expressions from Java. When applied to this
> problem really create a simple result:
>
> const category = data.category || switch (setting.incomeCode) {
> case TaxIncomeCode.RENTS_14 => PaymentCategory.RENT;
> case TaxIncomeCode.ROYALTIES_COPYRIGHTS_12 =>
> PaymentCategory.ROYALTIES;
> case TaxIncomeCode.INDEPENDENT_PERSONAL_SERVICE_17 =>
> PaymentCategory.SERVICES;
> default => PaymentCategory.OTHER;
> }
>
> Note; the instead of using the '->' as Java, continue to use => and with
> the understanding that the right hand side is fundamentally function.
> So similar things to this are natural, note this proposal should remove
> "fall through" breaks and allow for multiple cases as such.
>
> const quarter = switch (foo) {
> case "Jan", "Feb", "Mar" => "Q1";
> case "Apr", "May", "Jun" => "Q2";
> case "Jul", "Aug", "Sep" => "Q3";
> case "Oct", "Nov", "Dec" => { return "Q4" };
> default => { throw new Error("Invalid Month") };
> }
>
> Also compared this to the do expression proposal, it also provides a
> substantial simplification, but in a way that is more consistent with
> the existing language. In one of their examples they provide an example
> of the Redux reducer
> https://redux.js.org/basics/reducers#splitting-reducers -- this would be
> a switch expression implementation.
>
> function todoApp(state = initialState, action) => switch
> (action.type) {
> case SET_VISIBILITY_FILTER => { ...state, visibilityFilter:
> action.filter };
> case ADD_TODO => {
> ...state, todos: [
> ...state.todos,
> {
> text: action.text,
> completed: false
> }
> ]
> };
> case TOGGLE_TODO => {
> ...state,
> todos: state.todos.map((todo, index) => (index ===
> action.index) ? { ...todo, completed: !todo.completed } : todo)
> };
> default => state;
> }
>
>
>
> _______________________________________________
> es-discuss mailing list
> es-discuss@mozilla.org
> https://mail.mozilla.org/listinfo/es-discuss
>
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