first crack at extracting values from arrays by giving an index as a …

[dparadise28]

Description: What this PR does
goal is to extract values from arrays nested in deeper structures and values from within those array values

an example is provided in the added test

Benchmark before change:

docker run -v `pwd`:/go/src/github.com/buger/jsonparser -i -t jsonparser go test  -test.benchmem -bench JsonParser ./benchmark/  -benchtime 5s -v
testing: warning: no tests to run
PASS
BenchmarkJsonParserLarge-2                         50000            182450 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserMedium-2                       200000             33686 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualMedium-2          500000             18086 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserSmall-2                       2000000              3361 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualSmall-2          5000000              1905 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyStructSmall-2          3000000              2776 ns/op             176 B/op          7 allocs/op
ok      github.com/buger/jsonparser/benchmark   59.980s

**Benchmark after change**:
docker run -v `pwd`:/go/src/github.com/buger/jsonparser -i -t jsonparser go test  -test.benchmem -bench JsonParser ./benchmark/  -benchtime 5s -v
testing: warning: no tests to run
PASS
BenchmarkJsonParserLarge-2                         50000            183814 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserMedium-2                       200000             34856 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualMedium-2          500000             17943 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserSmall-2                       2000000              3403 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyManualSmall-2          5000000              1877 ns/op               0 B/op          0 allocs/op
BenchmarkJsonParserEachKeyStructSmall-2          3000000              2786 ns/op             176 B/op          7 allocs/op
ok      github.com/buger/jsonparser/benchmark   60.314s

[buger]

Looks really cool!

Did you tried to re-use existing ArrayEach method, instead of embedding own parser?

[dparadise28]

Thanks! I'm glad you like it. I'm working on something that will be using the hard work you and all the contributors put into your parser and I came across something i though would be useful so figured I'd see if i could contribute.

Reusing ArrayEach was actually my first instinct and then i decided to go with somewhat duplicate parsing logic in an effort to be a bit more efficient and not iterate through part of the slice twice given you cant break when your using array each. But given the code is definitely more readable and there is greater reuse in this approach I think your right on point. And maybe we can think of a way to break out of ArrayEach aft something is triggered in order to optimize the impl a bit further.

[rami-dabain]

for breaking from ArrayEach: #58 (comment) though haven't tried it yet

[buger]

Nailed it #77 !

Thank you for the first version! I had to completely rewrite it, and add support for EachKey.