Read-only chain of DafReaders. — ReadOnlyChainDaf • dafr

Produced by chain_reader(). Every format_* read falls through the chain in reverse order (last wins); writes raise.

Usage

ReadOnlyChainDaf(
  name = character(0),
  internal = new.env(parent = emptyenv()),
  cache = new.env(parent = emptyenv()),
  axis_version_counter = new.env(parent = emptyenv()),
  vector_version_counter = new.env(parent = emptyenv()),
  matrix_version_counter = new.env(parent = emptyenv()),
  dafs = list()
)

Arguments

name: Human-readable identifier for the Daf store.
internal: Internal per-store environment used by format backends to stash backend-specific state; reserved for package use.
cache: Three-tier cache environment (mapped / memory / query). See new_cache_env().
axis_version_counter: Environment tracking per-axis mutation counters; invalidates cached reads when an axis is modified.
vector_version_counter: Environment tracking per-vector mutation counters.
matrix_version_counter: Environment tracking per-matrix mutation counters.
dafs: Ordered list of base DafReaders.

Examples

base <- memory_daf(name = "base")
overlay <- memory_daf(name = "overlay")
ch <- chain_reader(list(base, overlay))
inherits(ch, "dafr::ReadOnlyChainDaf")
#> [1] TRUE