Builds on the ^:struct keyword-lookup hint:
- ^TypeName for records. A tag naming a defrecord/deftype now resolves to the
struct fast path: record instances are tables tagged :jolt/deftype (not
:jolt/type), so a raw keyword get is correct for them. A new host contract fn
record-type? detects a record by its ->Name constructor; a non-record tag
(^String, ^long, ...) is ignored, as before.
- (get m :k) and (get m :k default) now get the same inlined keyword lookup as
(:k m): the representation guard fast path when unhinted, and the bare get
when the subject is ^:struct/^Record. A variable/number/string key still
falls through to core-get. The two call shapes share one emitter
(emit-kw-lookup).
- JOLT_CHECK_HINTS=1 turns a violated hint into a clear runtime error (naming
the local and key) by keeping the guard and throwing on the tagged arm. It is
off by default with zero cost to normal builds (a hinted lookup still emits a
bare get), and is part of the image-cache fingerprint. This is the answer to
"a lying hint is silent": opt into checking during development.
- Docs: RFC 0004 records the design, soundness contract, and measurements; the
reader spec gains S12b (hints are semantically transparent; jolt recognizes
^:struct and ^Record as lookup-optimization assertions).
There is no Clojure keyword equivalent for "plain map / fast keyword access"
(Clojure hints are class names), so ^:struct stays a jolt-specific flag,
analogous to ^:dynamic.
Verified: conformance 335/335 in all three modes and the full jpm test pass; a
seeded ray-tracer render is byte-identical hinted vs unhinted; the struct-hint
test covers record hints, the get-form, inline propagation, and the checked-mode
error. Full render with hints holds at 13.3s -> 10.9s (1.22x).
A constant-keyword lookup (:k m) currently emits a guarded form,
(if (get m :jolt/type) (core-get m k) (get m k)), to tell a plain struct
(raw get is correct) from a phm/sorted/transient (needs core-get). On a
struct that guard is a second get, so the lookup costs ~36ns where a bare
get is ~20ns. Profiling the ray tracer (jolt-dad) showed keyword lookups are
~50% of a render and the guard is the only avoidable part, but dropping it
needs to know statically that the subject is a plain struct.
Type hints are exactly that information, and jolt already parses them and
otherwise ignores them. This wires one through: a local hinted ^:struct
asserts a plain struct/record map, so a (:k local) lookup on it skips the
guard and emits a bare get. The hint rides on the binding symbol into the
analyzer, which records it per-local and attaches it to :local IR nodes; the
back end reads it on the lookup subject. It also propagates through inlining:
when the inliner let-binds a non-trivial arg to a fresh local, it carries the
called fn's param hint onto that local, so lookups inside the spliced body
keep the bare path. This is a programmer assertion, like a Clojure type hint
(an inaccurate hint just makes the raw get return the wrong value, the same
contract as a wrong ^String), so it stays opt-in and off by default.
On the ray tracer (with inlining on) this is 13.3s to 10.9s, 1.22x, taking it
to 7.8x JVM from 9.4x after the inline pass. The unhinted path emits identical
code (the fast arm is just factored out), so nothing changes without hints.
Verified: a seeded full render produces an identical checksum hinted vs
unhinted; conformance 335/335 in all three modes and the full jpm test pass;
new test/integration/struct-hint-test.janet pins the guard removal, the
inline propagation, and that an accurate hint is correctness-preserving.
