can't get length of array if the path has a number as key ":4".

[Databingo]

suppose json is :
j := [0,1,2,3,{"4": {"test0":[1,2,3,"4"]}}]
run:
length := gjson.Get(j, "4.:4.test0.#").Int()
get 0;

but if change data key from number "4" to string "a":
j := [0,1,2,3,{"a": {"test0":[1,2,3,"4"]}}]
then run:
length := gjson.Get(j, "4.a.test0.#").Int()
get 4.

The different is the path where change :4 to a. Is this a problem or I miss something?

[Databingo]

and seems like can't insert number item in empty array:
sjson.Set("[]", 0, 0 )
return []

[volans-]

suppose json is :
j := [0,1,2,3,{"4": {"test0":[1,2,3,"4"]}]
run:
length := gjson.Get(j, "4.:4.test0.#").Int()
get 0;

The key in your JSON is just 4, not :4.
For the provided JSON the query should be 4.4.test0.#. If instead your JSON is modified to have a :4 key then your current query ( 4.:4.test0.# ) works fine.

[Databingo]

suppose json is :
j := [0,1,2,3,{"4": {"test0":[1,2,3,"4"]}}]
run:
length := gjson.Get(j, "4.:4.test0.#").Int()
get 0;

The key in your JSON is just 4, not :4. For the provided JSON the query should be 4.4.test0.#. If instead your JSON is modified to have a :4 key then your current query ( 4.:4.test0.# ) works fine.

Thank you but I think query .4 is for the 5th position of an array, so for a string "4" as key we need use ":4" to indicate it. Here is the document https://github.com/tidwall/sjson#path-syntax say:

"Normally number keys are used to modify arrays, but it's possible to force a numeric object key by using the colon character:"
{ "users":{ "2313":{"name":"Sara"}, "7839":{"name":"Andy"} } }
A colon path would look like:
"users.:2313.name" >> "Sara"

Finally I find out :4 is for sjson pacakge that modify json, not gson packege that query json, thanks a lot!
I chang to 4.4.test0.# then get the corrent length.

[volans-]

@Databingo but that's sjson documentation though and I don't see the same note on the gjson documentation. You can test what I've mentioned earlier in https://gjson.dev/

The first .4 returns the 5th element that is an object ( {"4": {"test0":[1,2,3,"4"]}}) and at that point an additional .4 selects the key with value 4. And there is no possible ambiguity because as per JSON specifications object keys can only be strings.

[Databingo]

@volans- Thanks a lot, I got it, why not author keep gjson same syntax ":4" with sjson in case someone use number as object key accidentally?

Maybe package could figure out that's an object so .4 only be a key rather than an index of array, but ".:4" is much easier for user to explicitly express his intention of a numeric key.

Finally I think no need because user no need to consider which situation(array index or object key) it is when use a number in query.

Still have another question: seems like sjson can't insert number item in an empty array:
sjson.Set("[]", 0, 0 ) return []

[volans-]

Sorry I'm not familiar with the sjson side of things, I'll leave that to @tidwall or others to answer.

[Databingo]

@volans- Thank you!

[tidwall]

@Databingo For sjson.Set("[]", 0, 0 ), the second param must be a string. https://go.dev/play/p/j3Zv32Op236

[Databingo]

@tidwall Thanks a lot, I got it!