Tape reading without alloc

Project.toml

@@ -1,7 +1,7 @@
 name = "JSON3"
 uuid = "0f8b85d8-7281-11e9-16c2-39a750bddbf1"
 authors = ["Jacob Quinn <[email protected]>"]
-version = "1.9.5"
+version = "1.10.0"
 
 [deps]
 Dates = "ade2ca70-3891-5945-98fb-dc099432e06a"

README.md

@@ -55,3 +55,41 @@ using StructTypes
 JSON3.@generatetypes json_string_sample
 JSON3.read(json_string, JSONTypes.Root)
 ```
+
+#### Non-allocating interface
+
+```julia
+json_string = """
+{
+    "a": 1,
+    "b": [1,2,3,5,8],
+    "c": {
+        "a": ["2"],
+    }
+}
+"""
+reader = JSON3.Reader()
+obj = JSON3.parse!(reader, json_string, JSON3.JSONObject) # returns a JSON3.JSONObject
+
+# method 1
+obj["a", Int64] # 1
+# method 2
+cursor = findcursor(obj, "a") # JSON3.Cursor
+item = obj[cursor, Int64] # 1
+# method 3
+field = first(obj)
+key(field) # "a", SubString
+value(field, Int64) # 1
+
+# Array
+collect(obj["b", JSON3.JSONArray{Int64}]) # [1,2,3,5,8]
+# Object
+obj["c", JSON3.JSONObject] # JSON3.JSONObject 
+
+# Data is accessed by iterating over the fields.
+# When fields are orders, it is possible to access them sequentially:
+cursor = findcursor(obj, "a") # JSON3.Cursor
+cursor2 = findcursor(obj, "b", cursor) # iterates from cursor
+obj[cursor2] # obj["b"] 
+
+```

benchmarks/lowlevel.jl

@@ -0,0 +1,39 @@
+using JSON3, BenchmarkTools
+
+str = """
+{
+    "a": 1,
+    "b" :2.1,
+    "c": 
+    "3",
+    "d": [1,2,3,5,8],
+    "e": [
+        1,"23",
+        [4,5]],
+    "f": {
+        "a": ["2"],
+        "b": 1
+    }
+}
+"""
+
+reader = JSON3.Reader()
+obj = JSON3.parse!(reader, str, JSON3.JSONObject)
+
+function f0(str)
+    x = JSON3.read(str)
+    x["f"]["b"]
+end
+
+function f1(reader, str)
+    obj = JSON3.parse!(reader, str, JSON3.JSONObject)
+    obj["f", JSON3.JSONObject]["b", Int64]
+end
+
+function f2(obj)
+    obj["f", JSON3.JSONObject]["b", Int64]
+end
+
+@benchmark f0($str)
+@benchmark f1($reader, $str)
+@benchmark f2($obj)

src/JSON3.jl

@@ -48,7 +48,7 @@ function populateinds!(x::Object)
         key = getvalue(Symbol, buf, tape, tapeidx, t)
         tapeidx += 2
         inds[key] = tapeidx
-        @inbounds tapeidx += gettapelen(Any, tape[tapeidx])
+        @inbounds tapeidx += gettapelen(tape[tapeidx])
         i += 1
     end
     return
@@ -64,7 +64,7 @@ function populateinds!(x::Array)
     i = 1
     while i <= len
         @inbounds inds[i] = tapeidx
-        @inbounds tapeidx += gettapelen(Any, tape[tapeidx])
+        @inbounds tapeidx += gettapelen(tape[tapeidx])
         i += 1
     end
     return
@@ -78,7 +78,7 @@ end
     tapeidx += 2
     @inbounds t = tape[tapeidx]
     x = Pair{Symbol, Any}(key, getvalue(Any, getbuf(obj), tape, tapeidx, t))
-    tapeidx += gettapelen(Any, t)
+    tapeidx += gettapelen(t)
     return x, (i + 1, tapeidx)
 end
 
@@ -149,7 +149,7 @@ function Base.iterate(arr::Array{T}, (i, tapeidx)=(1, 3)) where {T}
     tape = gettape(arr)
     @inbounds t = tape[tapeidx]
     val = getvalue(T, getbuf(arr), tape, tapeidx, t)
-    tapeidx += gettapelen(T, t)
+    tapeidx += gettapelen(t)
     return val, (i + 1, tapeidx)
 end
 
@@ -171,5 +171,6 @@ include("structs.jl")
 include("write.jl")
 include("pretty.jl")
 include("gentypes.jl")
+include("read_tape.jl")
 
 end # module