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If you don’t mix logic with I/O then why do you even need async-await as a language feature? I’m not disagreeing with you, but the whole point of async-await wa

• hinkley 4y ago
  IO callbacks don’t compose. That’s why everyone is switching to async await (that, and faddishness). This problem is amplified by mixing business logic and IO, so the motivation is in the wrong place and continues through the refactor because we’re solving only half the problem. Most of the interesting business logic is collating data from three or four places, and fetching that data sequentially is high latency. So you can do that part asynchronously and then present the input to sequential (pure) code that derives the answer. That pure code is very easy to unit test. The “problem” is now I have three kinds of code - IO, logic, and orchestration - and people intuit that this is more complicated than the bookkeeping they do and externalization onto others by mashing all three concerns together in one file, and then duplicate it with elaborate fakes in their tests. Which they are hesitant to write or others are hesitant to maintain, leading to low value, high effort tests.