wangrunji0408 commented on issue #11413:
URL: https://github.com/apache/datafusion/issues/11413#issuecomment-2348008054
@findepi
The `#[function]` macro doesn't process `ColumnarValue` as in datafusion.
Instead it always outputs an array value.
A new String object will be allocated if the `concat` function is defined as
above. However, you can prevent this by rewriting the function as follows,
where the result is written directly to the array buffer.
```rust
#[function("concat(string, string) -> string")]
#[function("concat(largestring, largestring) -> largestring")]
fn concat(lhs: &str, rhs: &str, output: &mut impl std::fmt::Write) {
write!(output, "{}{}", lhs, rhs).unwrap();
}
```
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