jayzhan211 commented on code in PR #14532:
URL: https://github.com/apache/datafusion/pull/14532#discussion_r1950526095
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datafusion/expr-common/src/signature.rs:
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@@ -227,25 +226,13 @@ impl Display for TypeSignatureClass {
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Hash)]
pub enum ArrayFunctionSignature {
- /// Specialized Signature for ArrayAppend and similar functions
- /// The first argument should be List/LargeList/FixedSizedList, and the
second argument should be non-list or list.
- /// The second argument's list dimension should be one dimension less than
the first argument's list dimension.
- /// List dimension of the List/LargeList is equivalent to the number of
List.
- /// List dimension of the non-list is 0.
- ArrayAndElement,
- /// Specialized Signature for ArrayPrepend and similar functions
- /// The first argument should be non-list or list, and the second argument
should be List/LargeList.
- /// The first argument's list dimension should be one dimension less than
the second argument's list dimension.
- ElementAndArray,
- /// Specialized Signature for Array functions of the form (List/LargeList,
Index+)
- /// The first argument should be List/LargeList/FixedSizedList, and the
next n arguments should be Int64.
- ArrayAndIndexes(NonZeroUsize),
- /// Specialized Signature for Array functions of the form (List/LargeList,
Element, Optional Index)
- ArrayAndElementAndOptionalIndex,
- /// Specialized Signature for ArrayEmpty and similar functions
- /// The function takes a single argument that must be a
List/LargeList/FixedSizeList
- /// or something that can be coerced to one of those types.
- Array,
+ /// A function takes at least one List/LargeList/FixedSizeList argument.
+ Array {
+ /// A full list of the arguments accepted by this function.
+ arguments: Vec<ArrayFunctionArgument>,
+ /// Whether any of the input arrays are modified.
+ mutability: ArrayFunctionMutability,
Review Comment:
> It is a bit confusing/unintuitive because we don't actually know anything
about the return type at this point, and the return type may have nothing to do
with the argument types
At the very least, the coerced types should be inferred from the signature
you provided. There may be a better design for this, but I haven’t come up with
an alternative idea yet.
> One thing I'm still confused about is, what if we wanted to define a
function that accepted FixedSizeList and returned List, or vice versa? Is that
possible? Does it even make sense?
I think both should be possible for datafusion and makes sense dependent on
what you want to do. FixedSizeList to List is common, List to FixedSizeList if
your function always output fixed size. Most of the existing function in
datafusion doesn't care about fixed size list, so convert it to list simplies
things
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