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  • h

    hackerham

    04/03/2017, 4:01 PM
    Two of my colleagues were somewhere nearby explosion and were questioned by police.
  • h

    hackerham

    04/03/2017, 4:01 PM
    And people are cooperating to get home together, because subway transportation is down
    ❤️ 1
  • c

    cedric

    04/03/2017, 9:21 PM
    @roberto.guerra There are quite a few downsides to 
    Reader
    , the first one is that it modifies all the signatures of the methods that need to read something from the config, e.g. from 
    Int
    to 
    Reader[C,Int]
    . That’s a huge breach in encapsulation that ripples through your whole code
  • r

    roberto.guerra

    04/03/2017, 9:23 PM
    yeah, but that can be resolved I think. Ideally, Reader should have a 
    map
    function that will lift those functions.
  • r

    roberto.guerra

    04/03/2017, 9:23 PM
    so you don’t have to modify any function signature
  • r

    roberto.guerra

    04/03/2017, 9:23 PM
    for example: 
    Reader.map(f)
    should do that
  • c

    cedric

    04/03/2017, 9:23 PM
    No that cannot be resolved, it’s the main “advantage” and point of the monad.
  • c

    cedric

    04/03/2017, 9:23 PM
    To make your functions pure.
  • c

    cedric

    04/03/2017, 9:24 PM
    They have to reflect they depend on 
    C
    .
  • c

    cedric

    04/03/2017, 9:24 PM
    So that this parameter can be passed instead of being injected, which is a side effect.
  • r

    roberto.guerra

    04/03/2017, 9:24 PM
    oh, ok. So it is not like lifting a function of ints to handle a function of Option(int), right?
  • r

    roberto.guerra

    04/03/2017, 9:24 PM
    because it is adding a new argument, and not just lifting them?
  • c

    cedric

    04/03/2017, 9:25 PM
    The purist approach is saying “Your function says it returns 
    Int
    but actually, it needs a config file to return that value, so it’s not pure. In order to be pure, that function needs to be passed a Config parameter so it can return an 
    Int
    from it. Hence the return type becomes 
    Reader[C, Int]
  • c

    cedric

    04/03/2017, 9:26 PM
    (which is basically a type alias for 
    C -> Int
    )
  • r

    roberto.guerra

    04/03/2017, 9:26 PM
    ok
  • c

    cedric

    04/03/2017, 9:27 PM
    So now picture that: deep inside your app, you have 
    getPort() = 1234
    . One day you decide “Ok now this comes from a config fille`. With 
    Reader
    , your function is now 
    getPort() : Reader[C, Int]
    and you need to modify all the callers
  • c

    cedric

    04/03/2017, 9:27 PM
    and their callers, and their callers. And to make matter worse, they now need to find out how to materialize that 
    Config
    parameter to pass it deep down to 
    getPort()
    .
  • c

    cedric

    04/03/2017, 9:28 PM
    Do you see how it breaks encapsulation? I just want a port number, I don’t care how you get it, just give me a port number.
  • c

    cedric

    04/03/2017, 9:28 PM
    And then one day you decide it’s no longer coming from a config file but from a database… blam, new signature change
  • c

    cedric

    04/03/2017, 9:29 PM
    Compare this to
    Copy code
    @Inject private config: Config

fun getPort() = config.port
  • c

    cedric

    04/03/2017, 9:29 PM
    All private, neat, expected 
    Int
    return type
  • c

    cedric

    04/03/2017, 9:29 PM
    want to change that one day? You callers won’t care, you’re just changing a private implementation detail
  • r

    roberto.guerra

    04/03/2017, 9:30 PM
    yeah, I see that. I personally don’t believe that these things should be injected deep in the code base tho
  • r

    roberto.guerra

    04/03/2017, 9:30 PM
    if you have a function that needs a to get a port, then it should be passed in as an argument
  • r

    roberto.guerra

    04/03/2017, 9:30 PM
    but yes, I see your point.
  • c

    cedric

    04/03/2017, 9:30 PM
    The only upside of 
    Reader
    is that it makes your code referentially transparent. But at an unacceptable price in my opinion
  • r

    roberto.guerra

    04/03/2017, 9:31 PM
    It tends to happen a lot in Clojure applications when using 
    component
  • c

    cedric

    04/03/2017, 9:31 PM
    Want to hear a third downside?
  • r

    roberto.guerra

    04/03/2017, 9:31 PM
    but I have to admit, it hasn’t happened to me in Clojure with 
    component
    , but other people seem to complain about that.
  • r

    roberto.guerra

    04/03/2017, 9:31 PM
    Sure
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