"for" will not build a list if you don't use its output value and that's
always the case if you have it between expressions, such as:
a = 1
for .... do ... end
b = 2
In this case, because you never use the result of for, we never build a
list. Enum.map will build a list regardless but I doubt it would matter to
the point of being noticeable.
*José Valim*
www.plataformatec.com.br
Skype: jv.ptec
Founder and Director of R&D
On Sun, Oct 30, 2016 at 3:04 PM, Luke Imhoff <[email protected]> wrote:
> Since the output of the `Enum.each`, `for`, and `Enum.map` is effectively
> ignored because only the entries in the defs_table (
> https://github.com/elixir-lang/elixir/blob/master/lib/
> elixir/src/elixir_def.erl#L207) matter, is there a performance benefit to
> replacing any `for` or `Enum.map` around `def` with `Enum.each` so the
> compilation doesn't spend the time and memory creating a list that'll just
> be throw away?
>
> On Sun, Oct 30, 2016 at 2:13 AM, José Valim <[email protected].
> br> wrote:
>
>> Def, like defmodule, module attributes and friends, is a side-effect. It
>> stores information in the module table. Returned quoted expressions
>> wouldn't quite work because we would need to collect them until the end.
>> Check the expanded code and it may clarify things a bit.
>>
>> On Sunday, October 30, 2016, Luke Imhoff <[email protected]> wrote:
>>
>>> I had thought that `def` returned (the equivalent [because it's really
>>> in elixir_bootstrap.erl] of a) quoted block and in order for a `def` to
>>> count in a loop, you'd need either a `for` comprehension, or `Enum.map`, so
>>> that the `quote` from each `def` is concatenated together to be merged into
>>> the caller's quoted form, but [Postgrex.Message.decode_auth_type/1 uses
>>> Enum.each](https://github.com/elixir-ecto/postgrex/blame/mas
>>> ter/lib/postgrex/messages.ex#L370-L372). How are all the `def`s inside
>>> the `Enum.each` being preserved when `Enum.each` doesn't return the value
>>> of each function call? This is related to https://github.com/KronicDe
>>> th/intellij-elixir/issues/472.
>>>
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>>
>> *José Valim*
>> www.plataformatec.com.br
>> Skype: jv.ptec
>> Founder and Director of R&D
>>
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