Using an @ attribute does not work, I think, but creating a decorate() macro does, see this gist.
That syntax is pretty OK, if you ask me:
decorate()
def i_am_instrumented(bar) do
..
Next step: creating macros to create decorator macros 
arjan
0
OvermindDL1
iex> quote do
...> @instrumented
...> def hello, do: "world"
...> end
{:__block__, [],
[{:@, [context: Elixir, import: Kernel], [{:instrumented, [], Elixir}]},
{:def, [context: Elixir, import: Kernel],
[{:hello, [context: Elixir], Elixir}, [do: "world"]]}]}
Nah, that is fine if it is only for the AST to go over, it only matters to set something if you want to access it post-ast.
You could always do something like this too:
defmodule SomeUserModule do
use Instrumented
@instrumented hello: 0
@instrumented anotherFun: 4
# ...
def hello, do: "world"
# .. lots of more functions
end
Hah, yep, could make a library for it all.
0
arjan
Doing just that! Right now I’m generating macros. Does not look so nice (no @) but it works pretty well. Let me know if you have a better way of doing this 
2
benwilson512
Author of Craft GraphQL APIs in Elixir with Absinthe
One this thread hasn’t really talked about is whether the decorator pattern is actually a good idea in Elixir. I’m not entirely convinced that it is.
With instrumentation for example very frequently the caller site is the thing that should care about whether or not a given function call is instrumented. If you mark a function as instrumented with a decorator then every call to it is gonna have some kind of side effect whether that is actually desired or not.
3
arjan
I partly agree with you… however, I use Java a lot which got my mind twisted in the wrong direction maybe
The use cases that I see right now are:
- For instrumentation, it is nice to use decorators because they allow you to turn it on or off with the addition/deletion of a single line of code.
- I also can see it working for Phoenix controllers, a bit like putting a plug in a controller but only for a single function call.
- Or for adding precondition checks to a function.
Anyway, I’ve wrapped it into a library: GitHub - arjan/decorator: Function decorators for Elixir · GitHub
0
OvermindDL1
I think it was the :trace module could allow you to hook functions, so you could define things to instrument based on module name and function name from the config or so?
0
arjan
Also found a way to do it with @ but downside there is that it breaks “regular” module attributes..
0
OvermindDL1
arjan
Because I do import Kernel, except: [@: 1]
and from my own @ macro I cant seem to call the Kernel.@ macro
0