Why using "|" in a map is calling update instead of put ?

[mG S]

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 ?

[charlott...@gmail.com]

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:

[charlott...@gmail.com]

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)

[mG S]

Any exemple about "avoid bugs but to allow potential optimizations" ? just curious actually...

[Ben Wilson]

Notably, this mailing list is for proposals for the development of the language. General questions are better suited for the forums, slack, irc, or other more general discussion areas.

[SEGALIS Morgan]

Sorry wasn’t aware of that...

--
You received this message because you are subscribed to a topic in the Google Groups "elixir-lang-core" group.
To unsubscribe from this topic, visit https://groups.google.com/d/topic/elixir-lang-core/HCHiY9ctjrg/unsubscribe.
To unsubscribe from this group and all its topics, send an email to elixir-lang-co...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/elixir-lang-core/ef39ecfc-8e92-4bfa-8272-b78e354b3528%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

--

Morgan SEGALIS