Composing Types with TypedStruct?

Questions / Help
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1

Background

Let’s say I have a TypedStruct that has some common fields:

typedstruct do
    @typedoc "A product."

    field(:item_id, String.t())
    field(:name, String.t())
    field(:brand, String.t())
  end

This is a product and because products can go on sale, I have another TypedStruct:

typedstruct do
    @typedoc "A sale."

    field(:item_id, String.t())
    field(:name, String.t())
    field(:brand, String.t())
    field(:price, number)
    field(:discount, boolean)
  end

Issue

Now, you are probably seeing there is some duplication here. Since a sale is a product with extra info, some of the fields are replicated.

A first attempt at a solution could be something like this:

typedstruct do
    @typedoc "A sale."

    field(:product, Product.t())
    field(:price, number)
    field(:discount, boolean)
  end

However, my use case does not allow for this. I must have a struct with exactly the same fields as Product.t() and a few extra. I cannot simply smash a product field into my sales struct.

Question

  • Is there a way to compose types using TypedStruct (or normal structs?)
  • If not, what do you think would be the solution with the least amount of copy/pasting for this issue?
2

Are you saying a sale contains a product (1)? Or is a sale something completely different from a product(2)?

If (2): They’re not the same so don’t try to do as if they’re the same.
In case of (1): I’m really interested as for why you can’t do what you proposed with product as part of sale?

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3

I would go for (1). A sale is not a product, but contains one.
I can’t follow the proposed solution because the generated Json file would not be compatible with the API I am integrating with.

4

I think the cleanest solution would be to write a custom encoder for the product: Jason.Encoder — jason v1.4.0

Although I would not mind this kind of duplication either.

It really depends on the domain and what sale and products are exactly.

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5

That sounds like you‘re missing a translation layer between your internal data model and the outside world.

2 Likes
6

Yes, that is the thing I am trying to build :smiley:
Would you go for duplication, for an implementation of the Jason encode protocol, or something else?

7

I’d go for the simplest to change option for things outside of your control, which would likely be duplication. Don’t try to abstract something other people are in charge off.

3 Likes