And it's also possible to update selected fields of an existing record.
This is all described in the docs:
iex(5)> r = bb()
{:bb, 1}
iex(6)> r1 = bb(r, a: 2)
{:bb, 2}
iex(7)> bb(r1, :a)
2
iex(8)> bb(a: x) = r1
{:bb, 2}
iex(9)> x
2
On Fri, Jan 3, 2020 at 11:19 AM Alexei Sholik <[email protected]> wrote:
> It's already possible to match on record's individual fields, you just
> need to import it:
>
> iex(2)> import B
> B
> iex(3)> bb(a: i) = bb()
> {:bb, 1}
> iex(4)> i
> 1
>
> On Fri, Jan 3, 2020 at 9:07 AM Kevin Johnson <[email protected]>
> wrote:
>
>> First proposal for 2020!
>>
>> Just like a `struct` is an extension over a `map` with its own dedicated
>> syntactic sugar, what prevents to regard a `record` to be an extension over
>> a `tuple` with syntactic sugar en par with that of a `struct`?
>>
>> When we introduce a `struct`:
>>
>> defmodule A do
>> defstruct a: 1
>> end
>>
>> Instead of interacting with it like:
>> %{__struct__: A, a: i} = a
>>
>> We can interact with it as:
>>
>> %A{a: i}= a
>>
>> and likewise we can pattern match the same on function arguments:
>>
>> def set(m =%A{},i), do:%{m|a: i}
>>
>>
>> According to the documentation <https://hexdocs.pm/elixir/Record.html> a
>> variety of `macro`s have already been introduced to abstract away from the
>> underlying `tuple` as a data structure.
>>
>> I am wondering if there would be any merit if a `Record` could be
>> accorded with its own special notation that would allow us to pattern match
>> accordingly?
>>
>> Currently the equivalent of the `set`-`method` above is to be written
>> using a `guard`, e.g.:
>> defmodule B do
>> import Record
>> defrecord(:bb, a: 1)
>>
>> def set(record, i) when is_record(record, :bb) do
>> bb(record, a: i)
>> end
>> end
>>
>>
>> and pattern matching on a specific value can only be done by resorting to
>> the underlying tuple implementation:
>>
>> require B
>> {:bb, i}= B.bb()
>>
>>
>> It would be nice if we could introduce a special notation such as:
>> ~bb{a: 1}
>>
>> So then we could:
>> def set(record = ~bb{}, i) do
>>
>> and:
>> require B
>> ~B.bb{a: i} = B.bb()
>>
>>
>>
>> These two aspects are the core aspects of my proposal. In addition to
>> this, I would like to highlight that it would be helpful if we could bridge
>> the gap even more by being able to do:
>> defmodule B do
>> import Record
>> defrecord(__MODULE__, a: 1)
>>
>> def set(record = ~__MODULE__{}, i) do
>> ...
>> which in itself is possible, but at the expense of losing access to the
>> underlying macros as enumerated in the documentation.
>>
>> You would not be able to do:
>> require B
>> # B()
>> # B.B()
>>
>> Also it would be nice to be able to update similar to a map:
>> defmodule B do
>> import Record
>> defrecord(__MODULE__, a: 1)
>>
>> def set(record = ~__MODULE__{}, i) do
>> ~__MODULE__{record | a: i}
>> end
>> end
>>
>>
>> These last two suggestions are mainly to illustrate how the end result
>> could potentially look like if we were to fully bridge the gap so to say,
>> but the most essential one is the pattern matching aspect detailed above.
>>
>> --
>> You received this message because you are subscribed to the Google Groups
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>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/elixir-lang-core/36e4c070-4efc-4641-8341-f3a95c71a905%40googlegroups.com
>> <https://groups.google.com/d/msgid/elixir-lang-core/36e4c070-4efc-4641-8341-f3a95c71a905%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
>
> --
> Best regards
> Alexei Sholik
>
--
Best regards
Alexei Sholik
--
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