Extend measure to allow optional function args

[CJPoll]

Erlang's :timer module already has a function for timing the duration
of a function. By using it, we can also enable passing arguments to the
passed-in function.

Examples:

measure("my_key", &Enum.map/2, [my_list, mapper_func])
measure("my_key", fn -> Enum.map(my_list, mapper_func) end) # Maintains backwards compatibility

This reports the duration of the map function, and returns the computed
value.

Optionally, we could also add a measure/4 function which takes a key,
module, function, and args.

measure("my_key", Enum, :map, [my_list, mapper_func])

See http://erlang.org/doc/man/timer.html#tc-1

[lexmag]

Great catch @CJPoll.
Let's skip addition of args in that PR.
Same result can be achieved without them.
Also, since these args will be optional, addition of options, which are optional as well, could be problematic: users will need to always provide args if they pass options.

[lexmag]

We can remove this TODO altogether.

[lexmag]

Let's move this calculation into the timing call:

{elapsed, result} = :timer.tc(fun)
timing(key, div(elapsed, 1000))
result

[CJPoll]

Sure thing

[CJPoll]

I'm a bit unsure what you mean in your overall feedback about options and args conflicting? Is that in regards to the idea of a measure/4 function?

measure/4 would probably look something like this:

def measure(key, module, function, args) when is_atom(module) and is_atom(function) and is_list(args) do
   {time, result} = :timer.tc(module, function, args)
   timing(key, div(time, 1000))
   result
end

Though you're right - measure(key, &Module.func/3, [arg1, arg2, arg3]) would allow us to do basically the same thing using only what's already been written in this PR.

Edited original post to include multiple examples.

[lexmag]

Sorry, my comment is indeed not clear enough.
I meant the following: I think we should not add measure/3 with optional args because it doesn't bring much, we can express any measure/3 call by using today's measure/2, like in your example:

measure("my_key", fn -> Enum.map(my_list, mapper_func) end)

Also it won't compose nicely with options from PR #6; call without function arguments will still require empty args provided if options is needed:

measure("my_key", fn -> ... end, [], [sample_rate: 0.5])

[CJPoll]

Ah - I wasn't aware of the other PR. That does make things difficult. Adding the args was the use case I was making this PR for. I suppose my apps can just define their own function which is equivalent to measure/3, so it's not a terrible burden on my part to implement in the application layer.

I'll push up the changes later today, then.

[CJPoll]

I believe that should remove the problem.

My apologies for the delay.

[lexmag]

Merged. Thank you @CJPoll. 💛