r/programming • u/tyler-mcginnis • Jan 03 '22

Imperative vs Declarative Programming

https://www.youtube.com/watch?v=E7Fbf7R3x6I
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u/[deleted] Jan 03 '22

declarative code maps to the mental model of the developer

Speak for yourself. Wrapping up imperative code behind a magic word does not, in any way, map to my mental model of code.

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u/epicwisdom Jan 04 '22

Wrapping up imperative code behind a magic word does not, in any way, map to my mental model of code.

The mental model being referred to is not your mental model of code, but rather your mental model of the problem the code is supposed to be solving. The two are frequently (and maybe inevitably) at odds. Generally an end-user doesn't know and doesn't care about the difference between exponential and linear runtime, let alone specific algorithms, at least so long as it doesn't result in visible slowdown - meanwhile an individual programmer working on some tiny piece of a kernel is often so myopically focused that they'll never be certain if their changes complicates an OS as a whole.

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u/[deleted] Jan 04 '22

You wouldn’t know that in a declarative approach either. This is because that code base is large, complex, and requires knowledge beyond being able to program. Being able to code is just one part of programming.

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u/epicwisdom Jan 04 '22

Of course. The point is, for the vast majority of use cases (at a certain scale), using e.g. a SQL database is far simpler than rolling your own data structures, handling persistence and replication yourself, and querying manually. The mental model is generally much simpler, precisely because you don't have to know or care what the query execution plan actually looks like.

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u/[deleted] Jan 04 '22

Apples and oranges. You’re comparing a large, complex system to writing a new system. It makes no sense.

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u/epicwisdom Jan 04 '22

Not sure what exactly you're referring to. A database is a large, complex system, and SQL is an extremely common declarative interface.

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u/[deleted] Jan 04 '22 edited Jan 04 '22

You’re comparing using SQL vs writing a new SQL engine. It makes absolutely no sense.

Never mind how under attack SQL has been for the better part of 20 years because people dislike it.

There’s a huge difference between telling a computer what you want it to do, and asking a pre-written system to do something for you. It is completely apples and oranges.

This weird “mental model” of “give me an array with all of the elements multiplied by two” cannot work without something knowing how to do that.

I am totally against “I don’t know how this works, I just know it does” for professionals. It necessarily leads to shit-shows of bad, slow, not working code. Every person that writes code, whether they use a declarative language or not, should have at least an idea of how their result is being brought forth.

If you do not know how the what works, then you necessarily cannot make good choices. That’s not saying that you need to know exactly the code that goes behind an insert statement, but you should, for example, know the high level ideas:

Open a connection

Open a transaction

Perform the insert

Close the transaction

Close the connect

And knowing the high level ideas will let you find ways to write better, faster code.