alamb commented on pull request #9531:
URL: https://github.com/apache/arrow/pull/9531#issuecomment-782837158
Hi @wqc200 -- I think the compiler issue in your example is due to the
reference of `self` in the wrapped closure.
If you pass in a `clone` of the string, then the example compiles and passes:
```rust
use std::sync::Arc;
use arrow::array::ArrayRef;
use arrow::array::StringArray;
use arrow::datatypes::DataType;
use arrow::util::display::array_value_to_string;
use datafusion::error::Result;
use datafusion::execution::context::ExecutionContext;
use datafusion::logical_plan::create_udf;
use datafusion::physical_plan::functions::ActualFunction;
use datafusion::physical_plan::functions::make_scalar_function;
#[derive(Debug, Clone)]
pub struct TestProvider {
db_name: String,
}
impl TestProvider {
pub fn try_new(db_name: &str) -> Result<Self> {
Ok(Self {
db_name: db_name.to_string(),
})
}
pub async fn test(&self, expected_name: String) -> Result<()> {
let mut ctx = ExecutionContext::new();
// implementation of `database()` function that returns expected_name
let captured_name = self.db_name.clone();
let database_function = move |_args: &[ArrayRef]| {
let res = StringArray::from(vec![Some(captured_name.as_str())]);
Ok(Arc::new(res) as ArrayRef)
};
ctx.register_udf(create_udf(
"database", // fuenction name
vec![], // input argument types
Arc::new(DataType::Utf8), // output type
ActualFunction::FuncImpl(make_scalar_function(database_function))), // function
implementation
);
let sql_results = ctx.sql(&format!("select
database()"))?.collect().await?;
let sql_result_col = array_value_to_string(sql_results[0].column(0),
0).unwrap();
assert_eq!(sql_result_col, expected_name);
Ok(())
}
}
#[tokio::test]
async fn test_func_provider_results() -> Result<()> {
let p = TestProvider::try_new("test")?;
p.test("test".to_string());
Ok(())
}
```
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