Optimize the common and special case where mm and dd are the same length, just swap in place. Avoids having to reparse the entire string.
For this case, it's about 30% faster and reduces allocations by about 15%.
This format is especially common, hence the reason to optimize for this case.
Also fix the case for ambiguous date/time in the mm:dd:yyyy format.
Previously, for ambiguous date strings, it was always calling parse twice even when the first parse would have been successful.
Refactor so that parsing isn't re-attempted unless the first parse fails ambiguously.
Benchmark results show that with RetryAmbiguousDateWithSwap(true), it's now about 6.5% faster (ns/op) and reduces allocated bytes by 3.4%.
Uses a memory pool for parser struct and format []byte
Uses a new go 1.20 feature to avoid allocations for []byte to string conversions in allowable cases.
go 1.20 also fixes a go bug for parsing fractional sec after a comma, so we can eliminate a workaround.
The remaining allocations are mostly unavoidable (e.g., time.Parse constructing a FixedZone location or part to strings.ToLower).
Results show an 89% reduction in allocated bytes for the big benchmark cases, and for some formats an allocation can be avoided entirely.
There is also a resulting 26% speedup in ns/op.
Details:
BEFORE:
cpu: 12th Gen Intel(R) Core(TM) i7-1255U
BenchmarkShotgunParse-12 19448 B/op 474 allocs/op
BenchmarkParseAny-12 4736 B/op 42 allocs/op
BenchmarkBigShotgunParse-12 1075049 B/op 24106 allocs/op
BenchmarkBigParseAny-12 241422 B/op 2916 allocs/op
BenchmarkBigParseIn-12 244195 B/op 2984 allocs/op
BenchmarkBigParseRetryAmbiguous-12 260751 B/op 3715 allocs/op
BenchmarkShotgunParseErrors-12 67080 B/op 1679 allocs/op
BenchmarkParseAnyErrors-12 15903 B/op 200 allocs/op
AFTER:
BenchmarkShotgunParse-12 19448 B/op 474 allocs/op
BenchmarkParseAny-12 48 B/op 2 allocs/op
BenchmarkBigShotgunParse-12 1075049 B/op 24106 allocs/op
BenchmarkBigParseAny-12 25394 B/op 824 allocs/op
BenchmarkBigParseIn-12 28165 B/op 892 allocs/op
BenchmarkBigParseRetryAmbiguous-12 37880 B/op 1502 allocs/op
BenchmarkShotgunParseErrors-12 67080 B/op 1679 allocs/op
BenchmarkParseAnyErrors-12 3851 B/op 117 allocs/op
Fix for this bug mentioned in https://github.com/araddon/dateparse/pull/134
Also, the other cases mentioned in this PR are not valid formats, so add them to the TestParseErrors test, to document that this is expected.
How golang parses date strings with respect to time zones and locations can be really confusing. Document the key points that need to be understood to properly interpret the results of parsing arbitrary date strings, which may or may not have explicit time zone name or offset information include the parsed date string.
