Add configurable cache modes and fallback policies for non-isbits types#34
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ChrisRackauckas merged 2 commits intoMar 30, 2026
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Replaces the boolean `FB` type parameter with two orthogonal configuration axes:
Cache modes (how fallback FunctionWrappers are cached):
- NoCache: dynamic dispatch every call (1 alloc, legacy behavior)
- SingleCache: cache one FunctionWrapper for last arg types (0 alloc on hit)
- DictCache: cache per arg type in a Dict (0 alloc, multi-type)
Fallback policies (when fallback is allowed):
- Strict: always error on mismatch (legacy Val{false})
- AllowAll: always fall back (legacy Val{true})
- AllowNonIsBits: fall back only for non-isbits types, error for isbits mismatches
Default is SingleCache + AllowNonIsBits, which provides zero-allocation
fallback for BigFloat, SparseConnectivityTracer, and similar non-isbits types
while still catching isbits type mismatches as bugs.
The key mechanism is lazily creating and caching a FunctionWrapper for the
actual argument types on first fallback hit. Subsequent calls use the cached
wrapper's ccall path with no extra allocations.
Legacy API (Val{true}/Val{false} and FunctionWrappersWrapper{FW,Bool})
is preserved for backward compatibility, mapping to AllowAll/Strict + NoCache.
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Breaking change: removes the boolean FB type parameter and Val{true}/Val{false}
API. The FunctionWrappersWrapper type now takes a fallback policy and cache
storage type as type parameters instead.
Cache modes (how fallback FunctionWrappers are cached):
- NoCache: dynamic dispatch every call (1 alloc per call)
- SingleCache: lazily cache a FunctionWrapper for last-seen arg types (0 alloc)
- DictCache: cache per arg type in a Dict (0 alloc, multi-type)
Fallback policies (when fallback is allowed):
- Strict: always error on type mismatch
- AllowAll: always fall back to original function
- AllowNonIsBits: fall back for non-isbits types, error for isbits mismatches
Default: SingleCache + AllowNonIsBits
Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Mar 30, 2026
FunctionWrappersWrappers v1.0.0 (SciML/FunctionWrappersWrappers.jl#34) adds configurable cache modes and fallback policies for non-isbits types. This is non-breaking — it strictly allows more types through the wrapper. Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com> Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
NoCache,SingleCache,DictCache) and fallback policies (Strict,AllowAll,AllowNonIsBits) toFunctionWrappersWrapperSingleCache+AllowNonIsBits— zero-allocation fallback for non-isbits types (BigFloat, SparseConnectivityTracer, etc.) while still catching isbits mismatchesVal{true}/Val{false}andFunctionWrappersWrapper{FW, Bool}APIsDesign
Two orthogonal configuration axes replace the boolean
FBtype parameter:Cache modes (how fallback
FunctionWrappers are cached):NoCacheobj[](arg...)every callSingleCacheFunctionWrapperfor last-seen arg typesDictCacheDictFallback policies (when fallback is allowed):
StrictVal{false})AllowAllVal{true})AllowNonIsBitsThe key mechanism: on first fallback hit, a
FunctionWrapper{Any, ActualArgTypes}is created and cached. Subsequent calls use the cached wrapper's ccall path — zero extra allocations, no type parameter on the function (no unwanted specialization).Benchmark results (from SciML/SciMLBase.jl#1301)
Float64 isbits match path: all configurations identical at ~19.5 ns, 0 allocs. No regression.
Backward compatibility
Legacy APIs are preserved and map to the new system:
FunctionWrappersWrapper(f, args, rets, Val{false}())→Strict+NoCacheFunctionWrappersWrapper(f, args, rets, Val{true}())→AllowAll+NoCacheFunctionWrappersWrapper{FW, false}(fwt)→Strict+NoCacheFunctionWrappersWrapper{FW, true}(fwt)→AllowAll+NoCacheTest plan
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