feat(write): TabularExport<T> — an export declared once with typed columns - #84
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… overload, a chunk selector
…om the import's fields
…or a plain sequence — flushed as it goes Also: Columns returns a read-only wrapper, so a caller cannot cast it back to an array and change the export.
… sheet faults the caller's writer; remove a stray backup file
… nothing per row, serves concurrent writes
…AnyInRange<char> boxed 96 bytes on every text cell
TextRules.Check ran on every text cell and called the generic
IndexOfAnyInRange('\uD800', '\uDFFF'), which allocates boxed chars on each
call: up to ~81 MB per million rows in the export test, in every format;
how much showed depended on tiered compilation, hence the varying failures.
A SearchValues over U+D800..U+DFFF finds the same surrogates with no
allocation. A million rows now allocate ~22 KB more than ten thousand
(per-chunk async state), in csv, xlsx and ods on net8.0 and net10.0.
… fails; reword the surrogate-check comment
…ns; rename the selector to itemsOf; name the real parameter for a null chunk; cover selector and cancellation failures
… document ArgumentException for a null chunk; spec states the measured per-cell cost
… one-off tiering allocation on Linux net10 failed the exact zero
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Part 4 of #67. Closes #73.
TabularExport.For<T>().Column(...).Build(): typed columns (text, integers, decimal, double, bool, DateTime, DateOnly, nullable), headers from typed import fields so an export maps back by header.IEnumerable<T>,IAsyncEnumerable<T>, chunks, or messages with a chunk selector (itemsOf) — e.g. a server stream of batches — flushing per chunk and when the buffer recommends it.SearchValues(the generic range search boxed 96 B per text cell at tier 0).TabularFile.Open→ import by header gives the same values.