Jordan, One question that I have lingering from pattern matching is why is the syntax so different? IMHO it is still a switch statement with a variation of the match on the case rather than a whole new construct.
Is there somewhere I can find a bit of discussion about the history of the syntax decisions? --David > On Feb 25, 2019, at 12:33 PM, Jordan Harband <ljh...@gmail.com> wrote: > > Additionally, https://github.com/tc39/proposal-pattern-matching - switch > statements are something I hope we'll soon be able to relegate to the dustbin > of history. > >> On Mon, Feb 25, 2019 at 6:01 AM David Koblas <da...@koblas.com> wrote: >> I quite aware that it’s covered in do expressions. Personally I find do >> expressions non-JavaScript in style and it’s also not necessarily going to >> make it into the language. >> >> Hence why I wanted to put out there the idea of switch expressions. >> >> --David >> >> >>> On Feb 25, 2019, at 5:28 AM, N. Oxer <bluesh...@gmail.com> wrote: >>> >>> Hi, >>> >>> This would be covered by 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 >> _______________________________________________ >> es-discuss mailing list >> es-discuss@mozilla.org >> https://mail.mozilla.org/listinfo/es-discuss
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