3 ms·

This was an interesting read for me, but I'm struggling to understand, from a design/organizational perspective, why solving the expression problem is a good th

This was an interesting read for me, but I'm struggling to understand, from a design/organizational perspective, why solving the expression problem is a good thing. If I don't try to solve the expression problem, I'm left with two common [OOP] implementation approaches: 1. A file for each type, within which all operations are also defined for that type. 2. A file for each type (POD), and a file for each operation which contains implementations for all types. With either implementation, I achieve a good deal of consistency. The questions of "where should I put this new code", "what is the responsibility of this file", or "where could I find the implementation of operator <x> on type <y> within the code repository" are easily answered. Solutions to the expression problem appear to mix these two approaches. The result seems to be much more loosely structured code. If I want to find the definition of ToString for type Constant, where do I look? It could either be in `src/types/Constant.code` or `src/operations/ToString.code` within my code repository. And as a result, it's no longer obvious what the full responsibilities of any file are within a structured repository without skimming the source. I've heard some brief discussion of extending libraries with both types and operators - for example, adding a new image format to an image processing library and also adding a new operation. But at that point, doesn't your new code belong in the library (where you can implement it using approach 1 or 2), rather than in application code?

lackbeard 10y ago
Sometimes you add a new protocol (or interface) and you really want some existing types to implement that protocol. Some languages make that impossible (or really really ugly) when you didn't define those existing types yourself. What if the + operator didn't exist in Java? Think about how you would add it. Now think about how would like to be able to add it. What language features would have to be added to Java to support that?
qznc 10y ago
The Expression Problem is a non-problem, if you can modify all your codebase. Just change the image processing library. You probably want to static type system so you quickly find all places, where you have to change something. The Expression Problem is ugly, if you cannot change the image processing library for some reason.

lackbeard 10y ago

Sometimes you add a new protocol (or interface) and you really want some existing types to implement that protocol. Some languages make that impossible (or really really ugly) when you didn't define those existing types yourself. What if the + operator didn't exist in Java? Think about how you would add it. Now think about how would like to be able to add it. What language features would have to be added to Java to support that?

qznc 10y ago

The Expression Problem is a non-problem, if you can modify all your codebase. Just change the image processing library. You probably want to static type system so you quickly find all places, where you have to change something. The Expression Problem is ugly, if you cannot change the image processing library for some reason.