Re: [PR] fix: allow to skip middle optional named parameters [datafusion]

["Jefffrey (via GitHub)" <gi...@apache.org>]

Jefffrey commented on PR #19308:
URL: https://github.com/apache/datafusion/pull/19308#issuecomment-3665334719

   One thing I'm not understanding, is that this PR seems to imply all arguments are now optional and any can be skipped, filling in skipped arguments with scalar `NULL`; this means it is up to the UDFs themselves to check which arguments were provided (and define which are required), and assume that any scalar `NULL`s mean the argument was missing (even if the caller passed in a scalar `NULL` themself), correct?
   
   For example if we had a UDF like so:
   
   ```
   name: custom_udf
   signatures:
     - prefix: string, length: i64
     - prefix: string, suffix: string, length: i64
   ```
   
   Technically here `suffix` is optional, and when calling the function if we call it two 2 arguments (string & i64) then we'd know that only 2 arguments were provided and the implementation of the UDF can branch based on that. However if we call with named arguments for `prefix` and `length` but still omit `suffix`:
   
   ```sql
   custom_udf(prefix => 'a', length => 1)
   ```
   
   We'd always have 3 arguments provided because `suffix` gets filled with null.
   
   - Technically I think this code wouldn't work on current main anyway, now that I think of it; though it would just cause an error


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