erratic-pattern commented on code in PR #10454:
URL: https://github.com/apache/datafusion/pull/10454#discussion_r1597448118
##########
datafusion/expr/src/expr.rs:
##########
@@ -1654,28 +1654,42 @@ fn fmt_function(
write!(f, "{}({}{})", fun, distinct_str, args.join(", "))
}
-fn create_function_name(fun: &str, distinct: bool, args: &[Expr]) ->
Result<String> {
- let names: Vec<String> =
args.iter().map(create_name).collect::<Result<_>>()?;
- let distinct_str = match distinct {
- true => "DISTINCT ",
- false => "",
- };
- Ok(format!("{}({}{})", fun, distinct_str, names.join(",")))
+fn write_function_name<'a>(
+ w: &'a mut (dyn Write + 'a),
Review Comment:
> Rather than using dynamic dispatch I think you can make this just a normal
generic function and make the code simpler and likely more performant
>
> Something like
>
> ```rust
> fn write_function_name<W: Write>(
> w: &mut W,
> ```
>
> I actually tried it locally and it seems to work well. Here is a PR
[erratic-pattern#1](https://github.com/erratic-pattern/arrow-datafusion/pull/1)
to this branch for your consideration
I didn't find a meaningful difference in performance here vs monomorphic
types (I tried `&mut String` explicitly in my testing, which is similar code to
the generic here). In fact
[`Formatter`](https://doc.rust-lang.org/src/core/fmt/mod.rs.html#254) in the
standard library also has an internal `dyn Write`, though it has an actual need
for ad-hoc polymorphism whereas we don't. I am guessing it gets optimized in
most cases, but it certainly wouldn't hurt to make it explicitly generic so I
agree with this change.
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