datafusion_functions/string/
chr.rs

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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

use std::any::Any;
use std::sync::{Arc, OnceLock};

use arrow::array::ArrayRef;
use arrow::array::StringArray;
use arrow::datatypes::DataType;
use arrow::datatypes::DataType::Int64;
use arrow::datatypes::DataType::Utf8;

use crate::utils::make_scalar_function;
use datafusion_common::cast::as_int64_array;
use datafusion_common::{exec_err, Result};
use datafusion_expr::scalar_doc_sections::DOC_SECTION_STRING;
use datafusion_expr::{ColumnarValue, Documentation, Volatility};
use datafusion_expr::{ScalarUDFImpl, Signature};

/// Returns the character with the given code. chr(0) is disallowed because text data types cannot store that character.
/// chr(65) = 'A'
pub fn chr(args: &[ArrayRef]) -> Result<ArrayRef> {
    let integer_array = as_int64_array(&args[0])?;

    // first map is the iterator, second is for the `Option<_>`
    let result = integer_array
        .iter()
        .map(|integer: Option<i64>| {
            integer
                .map(|integer| {
                    if integer == 0 {
                        exec_err!("null character not permitted.")
                    } else {
                        match core::char::from_u32(integer as u32) {
                            Some(integer) => Ok(integer.to_string()),
                            None => {
                                exec_err!("requested character too large for encoding.")
                            }
                        }
                    }
                })
                .transpose()
        })
        .collect::<Result<StringArray>>()?;

    Ok(Arc::new(result) as ArrayRef)
}

#[derive(Debug)]
pub struct ChrFunc {
    signature: Signature,
}

impl Default for ChrFunc {
    fn default() -> Self {
        Self::new()
    }
}

impl ChrFunc {
    pub fn new() -> Self {
        Self {
            signature: Signature::uniform(1, vec![Int64], Volatility::Immutable),
        }
    }
}

impl ScalarUDFImpl for ChrFunc {
    fn as_any(&self) -> &dyn Any {
        self
    }

    fn name(&self) -> &str {
        "chr"
    }

    fn signature(&self) -> &Signature {
        &self.signature
    }

    fn return_type(&self, _arg_types: &[DataType]) -> Result<DataType> {
        Ok(Utf8)
    }

    fn invoke(&self, args: &[ColumnarValue]) -> Result<ColumnarValue> {
        make_scalar_function(chr, vec![])(args)
    }

    fn documentation(&self) -> Option<&Documentation> {
        Some(get_chr_doc())
    }
}

static DOCUMENTATION: OnceLock<Documentation> = OnceLock::new();

fn get_chr_doc() -> &'static Documentation {
    DOCUMENTATION.get_or_init(|| {
        Documentation::builder()
            .with_doc_section(DOC_SECTION_STRING)
            .with_description(
                "Returns the character with the specified ASCII or Unicode code value.",
            )
            .with_syntax_example("chr(expression)")
            .with_sql_example(
                r#"```sql
> select chr(128640);
+--------------------+
| chr(Int64(128640)) |
+--------------------+
| 🚀                 |
+--------------------+ 
```"#,
            )
            .with_standard_argument("expression", Some("String"))
            .with_related_udf("ascii")
            .build()
            .unwrap()
    })
}