Decoder

A decoder for Option[A].

This is modeled as a separate, named, subtype because Option decoders often have special semantics around the handling of JNull. By having this as a named subtype, we premit certain optimizations that would otherwise not be possible. See circe-generic-extras for some examples.

Create a Decoder which assumes one already exists

Certain recursive data structures (particularly when generic) greatly benefit from being able to be written this way. See cats.Defer

Note: while a Decoder written using Decoder.recursive can prevent unneeded creation of Decoder instances when recursing, the resulting Decoder cannot be guaranteed to be stack-safe.

Decode a JSON value into a scala.math.BigDecimal.

Note that decoding will fail on some very large values that could in principle be represented as BigDecimals (specifically if the scale is out of the range of scala.Int when the unscaledValue is adjusted to have no trailing zeros). These large values can, however, be round-tripped through JsonNumber, so you may wish to use decodeJsonNumber in these cases.

Also note that because scala.scalajs.js.JSON parses JSON numbers into a floating point representation, decoding a JSON number into a BigDecimal on Scala.js may lose precision.

Decode a JSON value into a scala.math.BigInt.

Note that decoding will fail if the number has a large number of digits (the limit is currently 1 << 18, or around a quarter million). Larger numbers can be decoded by mapping over a scala.math.BigDecimal, but be aware that the conversion to the integral form can be computationally expensive.