as a side note, you can note that erlang has :maps.put (inserts/replace a
k/v) and :maps.update (only replaces an existing kv),
elixir mimics this by having Map.put for insert/replace and %{x | atom:
:atom} for replace (note that Map.update/4 has a different behaviour and is
too complex for this case where you simply want to set an specific value to
a map that should have the expected key)
On Tuesday, January 16, 2018 at 2:56:10 PM UTC-2, [email protected]
wrote:
>
> The syntax for updating maps (ie: `%{x | foo: :bar}`) assumes the key is
> already set on the map, this is to, not only, avoid bugs but to allow
> potential optimizations
>
> In https://hexdocs.pm/elixir/Map.html you can see that this is an
> expected behaviour
>
> > Maps also support a specific update syntax to update the value stored
> under *existing* atom keys:
>
> On Tuesday, January 16, 2018 at 2:16:24 PM UTC-2, mG S wrote:
>>
>> Hi everyone,
>>
>> Well the whole question fits in the subject...
>> I was wondering why the pipe operator used in a map was sugar for
>> Map.update and not Map.put
>>
>> iex(1)> m=%{foo: 1}
>> %{foo: 1}
>> iex(2)> %{m | bar: 2}
>> ** (KeyError) key :bar not found in: %{foo: 1}
>> (stdlib) :maps.update(:bar, 2, %{foo: 1})
>> (stdlib) erl_eval.erl:255: anonymous fn/2 in :erl_eval.expr/5
>> (stdlib) lists.erl:1262: :lists.foldl/3
>> iex(2)> %{m | foo: 2}
>> %{foo: 2}
>>
>>
>> I'm sure it has good reasons, but I'm a little puzzled on why ?
>>
>>
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