quinnj commented on code in PR #493:
URL: https://github.com/apache/arrow-julia/pull/493#discussion_r1428703277
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src/ArrowTypes/src/ArrowTypes.jl:
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@@ -170,11 +170,15 @@ overload is necessary.
A few `ArrowKind`s have/allow slightly more custom overloads for their
`fromarrow` methods:
* `ListKind{true}`: for `String` types, they may overload
`fromarrow(::Type{T}, ptr::Ptr{UInt8}, len::Int) = ...` to avoid
materializing a `String`
- * `StructKind`: must overload `fromarrow(::Type{T}, x...)` where individual
fields are passed as separate
+ * `StructKind`:
+ * May overload `fromarrow(::Type{T}, x...)` where individual fields are
passed as separate
positional arguments; so if my custom type `Interval` has two fields
`first` and `last`, then I'd overload like
`ArrowTypes.fromarrow(::Type{Interval}, first, last) = ...`. Note the
default implementation is
`ArrowTypes.fromarrow(::Type{T}, x...) = T(x...)`, so if your type
already accepts all arguments in a constructor
no additional `fromarrow` method should be necessary (default struct
constructors have this behavior).
+ * Alternatively, may overload `fromarrowstruct(::Type{T}, ::Val{fnames},
x...)`, where `fnames` is a tuple of the
Review Comment:
Sorry to be so slow in the review here; it might be worth adding another
example the docs here like we have above, something like:
```
So taking the example from before, if my arrow data happens to have the
`first` and `last` fields for my `Interval` type reversed, I could implement
`fromarrowstruct(::Type{Interval}, ::Val{(last, first}), last, first) =
Interval(first, last)`
```
I find concrete examples usually help drive home the core point of a new
feature.
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