scala - 如何使这些函数定义 D.R.Y.？

Question

我有多个函数定义来编写 Parquet 文件，但我宁愿有一个通用函数。如何使一项通用功能起作用？问题是一个通用函数返回错误could not find implicit value for parameter writerFactory: com.github.mjakubowski84.parquet4s.ParquetWriter.ParquetWriterFactory[Product]多种功能:

import com.github.mjakubowski84.parquet4s.ParquetWriter
import org.apache.parquet.hadoop.metadata.CompressionCodecName
import org.apache.parquet.hadoop.ParquetFileWriter
import java.time.format.DateTimeFormatter
import java.time.LocalDate

def writeParquetUnsegmented(rows: List[ACaseClass], date: String) = {
    val outPath = s"s3a://redacted/path-$date.parquet"
    ParquetWriter.writeAndClose(outPath,
                                rows,
                                    ParquetWriter.Options(
                                                        writeMode = ParquetFileWriter.Mode.OVERWRITE,
                                                        compressionCodecName = CompressionCodecName.SNAPPY
                                                        ))
}

def writeParquetSegmented(rows: List[BCaseClass], date: String) = {
    val outPath = s"s3a://redacted/path-$date.parquet"
    ParquetWriter.writeAndClose(outPath,
                                rows,
                                    ParquetWriter.Options(
                                                        writeMode = ParquetFileWriter.Mode.OVERWRITE,
                                                        compressionCodecName = CompressionCodecName.SNAPPY
                                                        ))
}

一功能:

def writeParquetSegmented(rows: List[Product], date: String) = {
    val outPath = s"s3a://redacted/path-$date.parquet"
    ParquetWriter.writeAndClose(outPath,
                                rows,
                                    ParquetWriter.Options(
                                                        writeMode = ParquetFileWriter.Mode.OVERWRITE,
                                                        compressionCodecName = CompressionCodecName.SNAPPY
                                                        ))
}

我也尝试了不同的函数签名并得到了同样的错误。

def writeParquetSegmented[A](rows: List[A], date: String)

def writeParquetSegmented[A :< RowParent](rows: List[A], date: String)

Answer 1

我会试试这个签名:

def writeParquetSegmented[A : ParquetWriterFactory](rows: List[A], date: String)

编译器会将 context bound [A : ParquetWriterFactory]进入错误消息提示的隐式参数。

def writeParquetSegmented[A](rows: List[A], date: String)(implicit pwf: ParquetWriterFactory)