Module: SimpleCov::Combine::IdentityInterner

Defined in:
lib/simplecov/combine/identity_interner.rb

Overview

Builds the raw-key => interned-identity caches the tuple combiners keep.

The cache maps a raw key to its interned identity on first sight and keeps it: the pairwise fold would otherwise re-derive the accumulator's identities on every one of its merges, always to the same answer.

Identities exist only to be combine's hash keys, and Array#hash is not memoized, so keying on the identity tuple itself would rehash its elements for every key of both sides of every merge. An Integer hashes as an immediate. Two keys share an id exactly when their identities are equal, so the string and array forms of one key still merge together.

Class Method Summary collapse

Class Method Details

.build ⇒ Object 



21
22
23
24
25
26
27
 
# File 'lib/simplecov/combine/identity_interner.rb', line 21

def build
  ids = {} #: Hash[::Array[untyped], Integer]
  Hash.new do |cache, key|
    identity = yield(key)
    cache[key] = ids[identity] ||= ids.size
  end
end