在解码器中考虑此功能:
final def decodeCollect[F[_], A](dec: Decoder[A], limit: Option[Int])(buffer: BitVector)(implicit cbf: Factory[A, F[A]]): Attempt[DecodeResult[F[A]]] = {
我真正需要的是dec:Vector [Decoder [A]],像这样:
final def decodeCollect[F[_], A](dec: Vector[Decoder[A]], limit: Option[Int])(buffer: BitVector)(implicit cbf: Factory[A, F[A]]): Attempt[DecodeResult[F[A]]] = {
处理具有不自我描述的字段的二进制格式。文件的开头是描述记录,这些记录来自字段大小,以后必须在数据记录中应用这些字段大小。因此,我想建立一个解码器列表并将其应用N次,其中N是解码器的数量。
我可以编写一个以decodeCollect为模型的新函数,但是它需要一个隐式Factory,因此我可能必须编译scodec库并添加它。
使用scodec库中存在的方法有没有更简单的方法?处理工厂的方法还是其他方法?
我终于在编解码器代码库中破解了一个解决方案。现在那扇门已经打开,我将添加所需的任何东西,直到成功为止。
final def decodeNCollect[F[_], A](dec: Vector[Decoder[A]])(buffer: BitVector)(implicit cbf: Factory[A, F[A]]): Attempt[DecodeResult[F[A]]] = {
val bldr = cbf.newBuilder
var remaining = buffer
var count = 0
val maxCount = dec.length
var error: Option[Err] = None
while (count < maxCount && remaining.nonEmpty) {
dec(count).decode(remaining) match {
case Attempt.Successful(DecodeResult(value, rest)) =>
bldr += value
count += 1
remaining = rest
case Attempt.Failure(err) =>
error = Some(err.pushContext(count.toString))
remaining = BitVector.empty
}
}
Attempt.fromErrOption(error, DecodeResult(bldr.result, remaining))
}
final def encodeNSeq[A](encs: Vector[Encoder[A]])(seq: collection.immutable.Seq[A]): Attempt[BitVector] = {
if (encs.length != seq.length)
return Attempt.failure(Err("encodeNSeq: length of coders and items does not match"))
val buf = new collection.mutable.ArrayBuffer[BitVector](seq.size)
((seq zip (0 until encs.length)): Seq[(A, Int)]) foreach { case (a, i) =>
encs(i).encode(a) match {
case Attempt.Successful(aa) => buf += aa
case Attempt.Failure(err) => return Attempt.failure(err.pushContext(buf.size.toString))
}
}
def merge(offset: Int, size: Int): BitVector = size match {
case 0 => BitVector.empty
case 1 => buf(offset)
case n =>
val half = size / 2
merge(offset, half) ++ merge(offset + half, half + (if (size % 2 == 0) 0 else 1))
}
Attempt.successful(merge(0, buf.size))
}
private[codecs] final class VectorNCodec[A](codecs: Vector[Codec[A]]) extends Codec[Vector[A]] {
def sizeBound = SizeBound(0, Some(codecs.length.toLong))
def encode(vector: Vector[A]) = Encoder.encodeNSeq(codecs)(vector)
def decode(buffer: BitVector) =
Decoder.decodeNCollect[Vector, A](codecs)(buffer)
override def toString = s"vector($codecs)"
}
def vectorOf[A](valueCodecs: Vector[Codec[A]]): Codec[Vector[A]] =
provide(valueCodecs.length).
flatZip { count => new VectorNCodec(valueCodecs) }.
narrow[Vector[A]]({ case (cnt, xs) =>
if (xs.size == cnt) Attempt.successful(xs)
else Attempt.failure(Err(s"Insufficient number of elements: decoded ${xs.size} but should have decoded $cnt"))
}, xs => (xs.size, xs)).
withToString(s"vectorOf($valueCodecs)")