Multi-focus counterpart to AvroPrism, carried on the BINARY WIRE FORM like the prism:
AvroTraversal[A] <: Optic[Array[Byte], Array[Byte], A, A, MultiFocus[PSVec]]
type X = (Array[Byte], Option[ElementSpans])
to resolves the prefix to an array-typed field, walks the array's block framing, and locates + slice-decodes the focus inside every element (AvroBinaryCursor.locateElements); from re-encodes each focus and splices all spans back in one pass. Avro's standard (positive-count) array framing carries no byte lengths, so per-element splices can change size freely; payloads whose array used the negative-count (byte-sized) framing are RE-FRAMED on write — the whole array region is rebuilt as one canonical positive-count block with the focus splices applied (AvroBinaryCursor.reframeArray). Same carrier as dev.constructive.eo.jsoniter.JsoniterTraversal (MultiFocus[PSVec]), so .foldMap / .all / .modify / .headOption / same-carrier .andThen light up from the standard extension catalogue.
Read semantics are "fold the focuses that exist": elements whose focus walk or slice decode refuses keep their bytes but leave the focus set (untouched on write). Whole-walk failure (bad prefix / non-array terminal / truncated bytes) yields no foci and from returns the input — silent, like every write-side refusal here (diagnostics live on record).
AvroPrism's '''Laws & preconditions''' section applies verbatim: laws hold up to canonical re-encoding of the focused slices, writes need decodable current focuses, and the payload must be encoded under exactly this traversal's reader schema.
The record-carried face — the Ior-bearing modify / getAll / place / transfer surface over IndexedRecord | Array[Byte] | String input — lives behind ONE factory: record (AvroRecordTraversal). Drilling (.field / .at / .union[Branch] / .fields / Dynamic selection) stays here, the single mechanism; drill first, flip last.
The Fields-vs-Leaf split lives entirely inside focus (per AvroFocus); the compatibility alias AvroFieldsTraversal points back here.
Build-then-observe across the build-output ⇄ read-input seam, preserving structure, on a shared carrierF. Flip self (it must be reversible — Accessor[F]andReverseAccessor[F], i.e. an Iso or Review over Direct) so it reads T from B, then andThenthat under the same carrier. The result is the full Optic[B, A, C, D, F], not a collapsed getter: its read capability follows the carrier (.get for Direct), and self's read focus A survives as the composite's write-back focus.
Build-then-observe across the build-output ⇄ read-input seam, preserving structure, on a shared carrierF. Flip self (it must be reversible — Accessor[F]andReverseAccessor[F], i.e. an Iso or Review over Direct) so it reads T from B, then andThenthat under the same carrier. The result is the full Optic[B, A, C, D, F], not a collapsed getter: its read capability follows the carrier (.get for Direct), and self's read focus A survives as the composite's write-back focus.
This is exactly self.reverse.andThen(that). The motivating case is ana.cross(cata): a Review (the unfold) crossed with a getter on the built S (the fold) — a (materializing) hylomorphism whose .get reads the folded value. When that sits on a different carrier (a Prism, a Fold, …), the cross-carrier cross overload below is selected instead.
Seam: that's source is self's T and its back-type is self's S.
Re-encode each focus and splice all spans back in one pass (re-framing the array region when the original framing was byte-sized); any refusal returns the input bytes.
Re-encode each focus and splice all spans back in one pass (re-framing the array region when the original framing was byte-sized); any refusal returns the input bytes.
The IndexedRecord-carried counterpart of this traversal — the Ior-bearing diagnostic surface (modify / getAll / place / transfer + *Unsafe) over IndexedRecord | Array[Byte] | String input:
The IndexedRecord-carried counterpart of this traversal — the Ior-bearing diagnostic surface (modify / getAll / place / transfer + *Unsafe) over IndexedRecord | Array[Byte] | String input:
transparent inline def selectDynamic(inline name: String): Any
Dynamic field sugar — basket.items.each.name lowers to .field(_.name) via the macro. An Avro field named like a real member of this class must be drilled with the explicit .field(_.x) form.
Dynamic field sugar — basket.items.each.name lowers to .field(_.name) via the macro. An Avro field named like a real member of this class must be drilled with the explicit .field(_.x) form.
Locate every element's focused span and slice-decode the focuses that exist; whole-walk failure yields no foci (and a None plan, so from passes the input through).
Locate every element's focused span and slice-decode the focuses that exist; whole-walk failure yields no foci (and a None plan, so from passes the input through).
ANY outer ∘ read-only inner — the inner is honestly one-way (T = Unit: a Getter, AffineFold, or Fold), so only the two READ sides matter and the composite collapses to the read-only join of their strengths via compose.ReadCompose (Getter / PickFold / ForgetFold).
ANY outer ∘ read-only inner — the inner is honestly one-way (T = Unit: a Getter, AffineFold, or Fold), so only the two READ sides matter and the composite collapses to the read-only join of their strengths via compose.ReadCompose (Getter / PickFold / ForgetFold).
A trait member (not an extension in the companion) deliberately: once a receiver is statically one of the fused concrete classes, its andThen member overloads enter resolution and Scala 3 never falls back to extension methods when they all fail — the collapse must be in the member overload set to be reachable without an expected-type ascription.
Only the inner's T is pinned to Unit; its B stays free (IB) even though read-only inners always have B = Unit. That keeps this overload strictly LESS specific than the same-carrier andThen above (which accepts every argument this one does whenever B = Unit at the receiver), so a same-carrier read-only ∘ read-only call resolves unambiguously to the AssociativeFunctor path and this one fires exactly on the cross-seam cells the generic member cannot type.
Compose with another optic under the shared carrier F. Requires AssociativeFunctor[F]. Cross-carrier composition (Lens → Optional, Lens → Traversal, …) goes through the Morph-summoning overload of this same method.
Compose with another optic under the shared carrier F. Requires AssociativeFunctor[F]. Cross-carrier composition (Lens → Optional, Lens → Traversal, …) goes through the Morph-summoning overload of this same method.
Attributes
Example
case class Address(street: String)
case class Person(address: Address)
val streetLens = lens[Person](_.address).andThen(lens[Address](_.street))