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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