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fix: respect preferMap for empty maps in the streaming decoder - #122
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The streaming decoder built empty maps with
buildMap([], 0, context, true), which forcesallString = trueand therefore always returns a plain object — even whenpreferMapis enabled. The non-streaming path already respectspreferMapfor empty maps (buildMap([], 0, context)), so a streamed empty map decoded to{}while the same bytes decoded non-streaming gavenew Map().This one-line change drops the forced
allString, so streaming empty maps now match the documented contract (preferMap→Map, otherwise a plain object).I first attempted a larger change that applied the iterative decoder's direct-map-build to the streaming path, but profiling showed it regresses streaming (~2–3%): the streaming state machine feeds values one at a time, where per-item branching and the larger map frame outweigh removing the single
buildMappass. So I reverted it and kept only this minimal consistency fix.4391 tests pass on Node 22/24/26.