You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: namespace.rs
    path of file: ./repos/polars/crates/polars-ops/src/chunked_array/strings
    
    the code of the file until where you have to start completion: use arrow::array::ValueSize;
use arrow::legacy::kernels::string::*;
#[cfg(feature = "string
    
    fn str_slice(&self, offset: &Series, length: &Series) -> PolarsResult<StringChunked> {
        let ca = self.as_string();
        let offset = offset.cast(&DataType::Int64)?;
        // We strict cast, otherwise negative value will be treated as a valid length.
        let length = length.strict_cast(&DataType::UInt64)?;

        Ok(substring::substring(ca, offset.i64()?, length.u64()?))
    }