The optimization may happen on the loader. Use erts_debug:df(Mod, Fun,
Arity) and see that.
On Mon, Jan 3, 2022 at 5:03 PM Wiebe-Marten Wijnja <w...@resilia.nl> wrote:
> I've been running my tests on Elixir v1.13.1 built for OTP24 with OTP
> 24.1.2.
> When decompiling the resulting BEAM bytecode, the anonymous functions are
> still visible.
>
> I will do some benchmarks to see how the resulting performance is. Maybe
> the JIT will do something which is not visible in the BEAM bytecode.
> On 03-01-2022 16:57, José Valim wrote:
>
> then/2 is a macro and the emitted code should be optimized from Erlang/OTP
> 24+.
>
> On Mon, Jan 3, 2022 at 4:28 PM w...@resilia.nl <w...@resilia.nl> wrote:
>
>> Since v1.12 we have the macro `Kernel.then(value, function)` which
>> expects an arity-1 function and will call it with the given value.
>>
>> This makes code which used to be written as follows:
>>
>> ```
>> def update(params, socket) do
>> socket =
>> socket
>> |> assign(:myvar, params["myvar"])
>> |> assign_new(:some_default, fn -> 42 end)
>>
>> {:noreply, socket}
>> end
>> ```
>>
>> more readable, by allowing it to be written as:
>>
>> ```
>> def update(params, socket) do
>> socket
>> |> assign(:myvar, params["myvar"])
>> |> assign_new(:some_default, fn -> 42 end)
>> |> then(&{:noreply, &1})
>> end
>> ```
>>
>> This pattern seems to be common in codebases using Elixir 1.12 and up (At
>> least according to anecdotal evidence).
>>
>> All is well. Except there is a little snag: The new code does not have
>> the same runtime characteristics (both in performance and in memory usage)
>> as `then`desugars to `(function).(value)`: An anonymous function is created
>> and immediately run (and then garbage collected soon after).
>>
>> The Erlang compiler is clever enough to optimize these immediately-called
>> anonymous functions away, but it will only do so when `@compile :inline` is
>> set in the given module, to not mess with the call stack that might be
>> returned when an exception is thrown.
>>
>> Now `@compile :inline` is quite the sledgehammer, as it will inline *all*
>> functions in the current module (as long as they are not 'too big', which
>> can also be configured, and only in the places where they are called
>> statically).
>> But since we're dealing with anonymous functions here which do not have
>> clear names, there is no way to predict the name one should pass to the
>> `@compile` option.
>>
>>
>> It seems like this situation could be improved, although I am not sure
>> how.
>>
>> Is there a way to mark these anonymous functions in some kind of way, to
>> allow only them to be inlined?
>> Or is there maybe a way to have the Elixir-compiler already inline common
>> patterns like a capture with a datatype, rather than relying on the Erlang
>> compiler for this?
>> Your input is greatly appreciated.
>>
>> ~Marten/Qqwy
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