How can I find out if a TJSONNumber is double or Integer?

Question

I am writing a general calls to store and retrieve data via JSON. So when loading the data from JSON I can verify that it is a TJSONNumber but lack a proper way to find out if it is integer or double. Currently I do it this way, but I guess there are better ways?

FDataStore: TDictionary<string, Variant>;


for index := 0 to Value.Count - 1 do begin
   Pair := Value.Pairs[Index];
   if Pair.JsonValue is TJSONNumber then
        try
          FDataStore.AddOrSetValue(Pair.JsonString.Value, (Pair.JsonValue as TJSONNumber).AsInt);
        except
          FDataStore.AddOrSetValue(Pair.JsonString.Value, (Pair.JsonValue as TJSONNumber).AsDouble);
        end;
end;

Answer 1

Unfortunately, TJSONNumber doesn't tell you the actual type, so you have to parse the original text to figure it out yourself.

For instance, by using TryStrToInt64() (rather than try..except), eg:

var
  IntValue: Int64;
  V: Variant;

if TryStrToInt64(TJSONNumber(Pair.JsonValue).Value, IntValue) then
begin
  if IntValue >= Min(Integer) and IntValue <= Max(Integer) then
    V := Integer(IntValue)
  else
    V := IntValue;
end else
  V := TJSONNumber(Pair.JsonValue).AsDouble);

FDataStore.AddOrSetValue(Pair.JsonString.Value, Value);

Alternatively, you could scan the JSON string for '.' and 'E' characters (the only non-digit characters allowed in a JSON number besides '+' and '-'), eg:

var
  V: Variant;

if LastDelimiter('.Ee', TJSONNumber(Pair.JsonValue).Value) = 0 then
begin
  var IntValue := TJSONNumber(Pair.JsonValue).AsInt64;
  if IntValue >= Min(Integer) and IntValue <= Max(Integer) then
    V := Integer(IntValue)
  else
    V := IntValue
end
else
  V := TJSONNumber(Pair.JsonValue).AsDouble;

FDataStore.AddOrSetValue(Pair.JsonString.Value, V);

Note that TJSONNumber is also convertible to UInt and UInt64, so you may want to consider handling those types, as well.