Add fixedsizearray trait and StaticArrays support#39
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Generalize the fixed-size array construction path so that any array
type that can't be grown via push! can be handled by pre-allocating a
Memory{T} buffer, filling it via setindex!, and converting to the
target type.
New public API:
- `fixedsizearray(::Type{T})`: trait for types needing pre-allocate+fill
- `discover_dims(style, ::Type{T}, source)`: type-based dimension discovery
- `arrayfromdata(::Type{T}, mem, dims)`: convert filled buffer to target type
- `FixedArrayClosure`: setindex!-based 1D fill closure
The StaticArraysCore extension overrides these to:
- Read dimensions from type parameters (no JSON scanning)
- Convert Memory to StaticArray via Tuple (native representation)
Closes JuliaIO/JSON.jl#429
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
The arrayfromdata method uses Memory in its signature, which only exists on Julia >= 1.11. Without the guard, the extension would fail to precompile on older Julia versions. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Use Vector{ET} as the pre-allocated buffer on Julia < 1.11 where
Memory does not exist. Add arrayfromdata(::Type, ::Vector, ::Tuple)
methods in both the main module and the StaticArraysCore extension
so the fixed-size array path works on all supported Julia versions.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
fixedsizearraytrait to generalize the pre-allocate +setindex!array construction path (currently only used forndims > 1arrays) to any fixed-size array typeStaticArraysCorepackage extension that enablesStructUtils.makeforSVector,SMatrix,MVector, and otherStaticArraytypesMemory{T}as the flat backing buffer on Julia 1.11+, with the existing growable path as fallbackMotivation
StructUtils.makearrayassumes all 1D arrays are growable (push!intoT(undef, 0)). This fails forStaticArrayswhich are fixed-size and immutable. Thendims > 1path already uses a pre-allocate +setindex!approach — this PR generalizes that pattern.Closes JuliaIO/JSON.jl#429
New public API
fixedsizearray(::Type{T})discover_dims(style, ::Type{T}, source)arrayfromdata(::Type{T}, mem, dims)Memorybuffer to target type TFixedArrayClosuresetindex!-based 1D fill closure (vspush!-basedArrayClosure)How it works
For
fixedsizearraytypes on Julia 1.11+:discover_dimsgets dimensions (from type params for StaticArrays, source scan for regular Matrix)Memory{eltype(T)}(undef, prod(dims))allocates a flat bufferFixedArrayClosurefills via linearsetindex!; nD:MultiDimClosurefills via reshaped viewarrayfromdataconverts the filled Memory to the target typeThe StaticArraysCore extension (3 methods):
fixedsizearray(::Type{<:StaticArray}) = truediscover_dimsreads dimensions from type parameters (no source scanning)arrayfromdataconverts viaT(Tuple(mem))(StaticArrays' native representation)Test plan
Pkg.test())JSON.parse("[1,2,3]", SVector{3,Int})works🤖 Generated with Claude Code