Add struct field + associated tags caching

[deankarn]

More Optimizations!

• This essentially reduces the number of cache tag lookups for a structs fields to one.

What will I notice most!

Faster Struct, especially complex struct, validation!

New Benchmarks

$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkFieldSuccess-4                             10000000           162 ns/op           0 B/op          0 allocs/op
BenchmarkFieldFailure-4                              2000000           678 ns/op         400 B/op          4 allocs/op
BenchmarkFieldDiveSuccess-4                           500000          3079 ns/op         480 B/op         27 allocs/op
BenchmarkFieldDiveFailure-4                           300000          3584 ns/op         880 B/op         31 allocs/op
BenchmarkFieldCustomTypeSuccess-4                    5000000           345 ns/op          32 B/op          2 allocs/op
BenchmarkFieldCustomTypeFailure-4                    2000000           650 ns/op         400 B/op          4 allocs/op
BenchmarkFieldOrTagSuccess-4                         1000000          1188 ns/op          16 B/op          1 allocs/op
BenchmarkFieldOrTagFailure-4                         1000000          1088 ns/op         432 B/op          6 allocs/op
BenchmarkStructLevelValidationSuccess-4              2000000           689 ns/op         160 B/op          6 allocs/op
BenchmarkStructLevelValidationFailure-4              1000000          1290 ns/op         592 B/op         11 allocs/op
BenchmarkStructSimpleCustomTypeSuccess-4             2000000           911 ns/op          80 B/op          5 allocs/op
BenchmarkStructSimpleCustomTypeFailure-4             1000000          1446 ns/op         624 B/op         11 allocs/op
BenchmarkStructPartialSuccess-4                      1000000          1221 ns/op         384 B/op         10 allocs/op
BenchmarkStructPartialFailure-4                      1000000          1764 ns/op         800 B/op         15 allocs/op
BenchmarkStructExceptSuccess-4                       2000000           941 ns/op         336 B/op          7 allocs/op
BenchmarkStructExceptFailure-4                       1000000          1237 ns/op         384 B/op         10 allocs/op
BenchmarkStructSimpleCrossFieldSuccess-4             2000000           970 ns/op         128 B/op          6 allocs/op
BenchmarkStructSimpleCrossFieldFailure-4             1000000          1560 ns/op         560 B/op         11 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldSuccess-4  1000000          1542 ns/op         176 B/op          9 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldFailure-4  1000000          2147 ns/op         608 B/op         14 allocs/op
BenchmarkStructSimpleSuccess-4                       2000000           847 ns/op          48 B/op          3 allocs/op
BenchmarkStructSimpleFailure-4                       1000000          1497 ns/op         624 B/op         11 allocs/op
BenchmarkStructSimpleSuccessParallel-4               5000000           257 ns/op          48 B/op          3 allocs/op
BenchmarkStructSimpleFailureParallel-4               2000000           586 ns/op         624 B/op         11 allocs/op
BenchmarkStructComplexSuccess-4                       300000          5104 ns/op         496 B/op         29 allocs/op
BenchmarkStructComplexFailure-4                       200000          9840 ns/op        3400 B/op         71 allocs/op
BenchmarkStructComplexSuccessParallel-4              1000000          1540 ns/op         496 B/op         29 allocs/op
BenchmarkStructComplexFailureParallel-4               500000          3478 ns/op        3400 B/op         71 allocs/op

Old Benchmarks

$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkFieldSuccess-4                             10000000           163 ns/op           0 B/op          0 allocs/op
BenchmarkFieldFailure-4                              2000000           673 ns/op         400 B/op          4 allocs/op
BenchmarkFieldDiveSuccess-4                           500000          3019 ns/op         480 B/op         27 allocs/op
BenchmarkFieldDiveFailure-4                           500000          3553 ns/op         880 B/op         31 allocs/op
BenchmarkFieldCustomTypeSuccess-4                    5000000           347 ns/op          32 B/op          2 allocs/op
BenchmarkFieldCustomTypeFailure-4                    2000000           645 ns/op         400 B/op          4 allocs/op
BenchmarkFieldOrTagSuccess-4                         1000000          1177 ns/op          16 B/op          1 allocs/op
BenchmarkFieldOrTagFailure-4                         1000000          1093 ns/op         432 B/op          6 allocs/op
BenchmarkStructLevelValidationSuccess-4              2000000           702 ns/op         160 B/op          6 allocs/op
BenchmarkStructLevelValidationFailure-4              1000000          1279 ns/op         592 B/op         11 allocs/op
BenchmarkStructSimpleCustomTypeSuccess-4             1000000          1010 ns/op          80 B/op          5 allocs/op
BenchmarkStructSimpleCustomTypeFailure-4             1000000          1544 ns/op         624 B/op         11 allocs/op
BenchmarkStructPartialSuccess-4                      1000000          1249 ns/op         400 B/op         11 allocs/op
BenchmarkStructPartialFailure-4                      1000000          1797 ns/op         816 B/op         16 allocs/op
BenchmarkStructExceptSuccess-4                       2000000           927 ns/op         368 B/op          9 allocs/op
BenchmarkStructExceptFailure-4                       1000000          1259 ns/op         400 B/op         11 allocs/op
BenchmarkStructSimpleCrossFieldSuccess-4             1000000          1076 ns/op         128 B/op          6 allocs/op
BenchmarkStructSimpleCrossFieldFailure-4             1000000          1623 ns/op         560 B/op         11 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldSuccess-4  1000000          1582 ns/op         176 B/op          9 allocs/op
BenchmarkStructSimpleCrossStructCrossFieldFailure-4  1000000          2139 ns/op         608 B/op         14 allocs/op
BenchmarkStructSimpleSuccess-4                       1000000          1040 ns/op          48 B/op          3 allocs/op
BenchmarkStructSimpleFailure-4                       1000000          1683 ns/op         624 B/op         11 allocs/op
BenchmarkStructSimpleSuccessParallel-4               5000000           356 ns/op          48 B/op          3 allocs/op
BenchmarkStructSimpleFailureParallel-4               2000000           831 ns/op         624 B/op         11 allocs/op
BenchmarkStructComplexSuccess-4                       200000          6738 ns/op         512 B/op         30 allocs/op
BenchmarkStructComplexFailure-4                       200000         11387 ns/op        3415 B/op         72 allocs/op
BenchmarkStructComplexSuccessParallel-4               500000          2330 ns/op         512 B/op         30 allocs/op
BenchmarkStructComplexFailureParallel-4               300000          4857 ns/op        3416 B/op         72 allocs/op