add [1..2] for JArray (#18525)

* add [1..2] for JArray
* fix BackwardsIndex to int
* fix for BackwardsIndex
* fix for assert node kind check
* fix variable name
* Update lib/pure/json.nim
* fix for when x.a is BackwardsIndex

Co-authored-by: itsumura-h <dumblepy@mail.com>
Co-authored-by: Dominik Picheta <dominikpicheta@googlemail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/lib/pure/json.nim b/lib/pure/json.nim
index d5bbb86b8..85c3393b2 100644
--- a/lib/pure/json.nim
+++ b/lib/pure/json.nim
@@ -531,6 +531,24 @@ proc `[]`*(node: JsonNode, index: BackwardsIndex): JsonNode {.inline, since: (1,
 
   `[]`(node, node.len - int(index))
 
+proc `[]`*[U, V](a: JsonNode, x: HSlice[U, V]): JsonNode =
+  ## Slice operation for JArray.
+  ##
+  ## Returns the inclusive range `[a[x.a], a[x.b]]`:
+  runnableExamples:
+    import json
+    let arr = %[0,1,2,3,4,5]
+    doAssert arr[2..4] == %[2,3,4]
+    doAssert arr[2..^2] == %[2,3,4]
+    doAssert arr[^4..^2] == %[2,3,4]
+
+  assert(a.kind == JArray)
+  result = newJArray()
+  let xa = (when x.a is BackwardsIndex: a.len - int(x.a) else: int(x.a))
+  let L = (when x.b is BackwardsIndex: a.len - int(x.b) else: int(x.b)) - xa + 1
+  for i in 0..<L:
+    result.add(a[i + xa])
+
 proc hasKey*(node: JsonNode, key: string): bool =
   ## Checks if `key` exists in `node`.
   assert(node.kind == JObject)