Hi,
thanks for the suggestion, but I think you are answering to a different
problem than the one I had in mind, I'll try to be more clear to avoid
confusion.
In my use case, I have a lot of fields, which usually can be kept with
their default values, but some of them aren't. So not all customers need
names. Maybe a better example of the code I want to write would be:
type alias Customer =
{ id : Int,
name : String ,
occupation : String,
nickname : String,
height : Float,
-- Lots of other stuff
}
defaultCustomer : Int -> Customer
defaultCustomer id =
{ id = id,
name = "",
occupation = "",
nickname "N/A",
height : 1.6,
-- lots of other initialization
}
[
{ (defaultCustomer 1) | name = "Smith", occupation = "Clerk" },
{ (defaultCustomer 2) | name = "Jones" }
{ (defaultCustomer 3) | nickname = "R2-D2", height = 0.5 }
]
Martin
On Monday, 12 September 2016 17:50:21 UTC+2, Nick H wrote:
>
> In this case, I think the best thing to do would be to make a construction
> function that takes a name as well as an id.
>
> defaultCustomer : Int -> String -> Customer
> defaultCustomer id name =
> { id = id,
> , name = name,
> -- lots of other initialization
> }
>
> You constructor function should never return an incomplete/invalid record.
> If your customers always need names, make sure they always get names!
>
>
>
> On Sun, Sep 11, 2016 at 4:44 AM, Martin Cerny <[email protected]
> <javascript:>> wrote:
>
>> Hi,
>> hope its polite to bump up an old thread like this - if not, please
>> accept my apologies. I have been struggling with the record update syntax
>> for a while and wanted to share another use case which I think could be
>> made better.
>> So let's say I want to populate a list of objects of the same type which
>> have a lot of properties, most of which are kept default, e.g.
>>
>> type alias Customer =
>> { id : Int,
>> Name : String ,
>> -- Lots of other stuff
>> }
>>
>> and I have a "constructor" function to build instances with default
>> values, but never forget to fill in the id, e.g.
>>
>> defaultCustomer : Int -> Customer
>> defaultCustomer id =
>> { id = id,
>> Name = "",
>> -- lots of other initialization
>> }
>>
>> now I would like to write things like
>> [
>> { (defaultCustomer 1) | Name = "Smith" },
>> { (defaultCustomer 2) | Name = "Jones" }
>> ]
>>
>> Which is not possible.
>>
>> Now I have two options:
>> a) do not use a "constructor" and always write the records in full (not
>> nice since they have a lot of fields which are mostly left default)
>> b) just have a template defaultCostumer : Customer and hope I will never
>> forget to fill in the id (used in messages)
>> c) have a long "let" clause before defining the list
>>
>> Neither of which seems nice.
>>
>> I'll probably go with b), but if anyone has a nice suggestion how to
>> enforce filling in a record in this way with the current syntax it would be
>> very welcome.
>>
>> And thanks for the work on elm - I am learning it and having fun with it!
>>
>> Martin
>>
>>
>>
>>
>>
>> but I tried to figure out where on GitHub should this be discussed and
>> kind of failed...
>> (is it https://github.com/elm-lang/elm-plans/issues/16 or
>>
>> On Saturday, 26 July 2014 18:08:22 UTC+2, Jeff Smits wrote:
>>>
>>> Yeah, I really want this feature. But I guess I forgot about the "code
>>> comparison".
>>>
>>> @Evan: can you say more concretely what kind of code comparison you want
>>> to see before moving forward on this feature?
>>>
>>> On Sat, Jul 26, 2014 at 2:26 PM, David Sargeant <[email protected]>
>>> wrote:
>>>
>>>> Seems a little strange that the following does not work:
>>>>
>>>> { {} | attrs = [1] }
>>>>
>>>> I know it's not really useful, but I guess it goes back to the issue of
>>>> allowing arbitrary expressions to the left of the vertical bar.
>>>>
>>>> --
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>>>>
>>>
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>
>
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