Option support in toPreserves and fromPreserves

preserves.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version = "20240102"
+version = "20240103"
 author        = "Emery Hemingway"
 description   = "data model and serialization format"
 license       = "Unlicense"

src/preserves.nim

@@ -142,15 +142,6 @@ proc `&`*(x: Value; y: seq[Value]): Value =
     raise newException(ValueError, "cannot concatenate to non-sequence value")
   result = Value(kind: pkSequence, sequence: x.sequence & y)
 
-proc getOrDefault(pr, key: Value): Value =
-  ## Retrieves the value of `pr[key]` if `pr` is a dictionary containing `key`
-  ## or returns the `#f` Preserves value.
-  if pr.kind == pkDictionary:
-    for (k, v) in pr.dict:
-      if key == k:
-        result = v
-        break
-
 proc pop*(pr: var Value; key: Value; val: var Value): bool =
   ##  Deletes the `key` from a Preserves dictionary.
   ## Returns true, if the key existed, and sets `val` to the mapping
@@ -440,9 +431,15 @@ proc toPreserves*[T](x: T): Value {.gcsafe.} =
     elif T.hasCustomPragma(preservesDictionary):
       result = initDictionary()
       for key, val in x.fieldPairs:
-        var pr = fieldToPreserve(key, val)
+        when val is Option:
-        applyEmbed(key, pr)
+          if val.isSome:
-        result[toSymbol(key)] = pr
+            var pr = fieldToPreserve(key, val.get)
+            applyEmbed(key, pr)
+            result[key.toSymbol] = pr
+        else:
+          var pr = fieldToPreserve(key, val)
+          applyEmbed(key, pr)
+          result[key.toSymbol] = pr
       sortDict(result)
     else:
       {.warning: "failed to preserve object " & $T .}
@@ -491,6 +488,9 @@ proc toPreservesHook*[A, B](table: Table[A, B]|TableRef[A, B]): Value =
     result[toPreserves(k)] = toPreserves(v)
   sortDict(result)
 
+proc toPreservesHook*(o: Option): Value =
+  o.get.toPreserves
+
 proc fromAtom*[T](v: var T; a: ATom): bool =
   if T is Atom:
     v = a
@@ -715,12 +715,17 @@ proc fromPreserves*[T](v: var T; pr: Value): bool {.gcsafe.} =
       if pr.isDictionary:
         result = true
         var i: int
-        for key, _ in fieldPairs(v):
+        for key, field in fieldPairs(v):
-          let val = pr.getOrDefault(toSymbol(key))
-          result = result and fieldFromPreserve(
-            key, v.dot(key), val)
           if not result: break
-          inc i
+          let val = step(pr, key.toSymbol)
+          when field is Option:
+            if val.isSome:
+              discard fieldFromPreserve(key, v.dot(key), val.get)
+          else:
+            inc i
+            result = result and val.isSome
+            if result:
+              result = result and fieldFromPreserve(key, v.dot(key), val.get)
         result = result and (i <= pr.len)
     elif T.hasCustomPragma(preservesOr):
       for kind in typeof(T.orKind):
@@ -740,9 +745,11 @@ proc fromPreserves*[T](v: var T; pr: Value): bool {.gcsafe.} =
         result = true
         var i: int
         for key, _ in fieldPairs(v):
-          let val = pr.getOrDefault(toSymbol(key))
-          result = result and fieldFromPreserve(key, v.dot(key), val)
           if not result: break
+          let val = step(pr, key.toSymbol)
+          result = result and val.isSome
+          if result:
+            result = result and fieldFromPreserve(key, v.dot(key), val.get)
           inc i
         result = result and (i <= pr.len)
   else:
@@ -811,6 +818,12 @@ proc fromPreservesHook*[A,B](t: var (Table[A,B]|TableRef[A,B]); pr: Value): bool
         break
       t[move a] = move b
 
+proc fromPreservesHook*[T](opt: var Option[T]; pr: Value): bool =
+  opt = some(default T)
+  result = opt.get.fromPreserves(pr)
+  if not result:
+    opt = none(T)
+
 when isMainModule:
   var t: Table[int, string]
   var pr = t.toPreservesHook()

tests/test_conversions.nim

@@ -17,11 +17,13 @@ suite "conversions":
       a: int
       b: seq[int]
       c {.preservesEmbedded.}: Bar
+      d: Option[bool]
+      e: Option[bool]
     let
-      c = Foobar(a: 1, b: @[2], c: ("ku", ))
+      c = Foobar(a: 1, b: @[2], c: ("ku", ), e: some(true))
       b = toPreserves(c)
       a = preservesTo(b, Foobar)
-    check($b == """{a: 1 b: [2] c: #!["ku"]}""")
+    check($b == """{a: 1 b: [2] c: #!["ku"] e: #t}""")
     check(a.isSome)
     if a.isSome: check(get(a) == c)
     check(b.kind == pkDictionary)