apple/pkl · error · FormatException

double

Error message

double

What it means

FormatException("double", value.getClass()) is thrown by DependencyMetadata.parsePObject when the `value` field of a DataSize entry is present but not a JSON number (Double). DataSize values must be numeric; strings like "10mb" or booleans are rejected. It indicates a wrong-typed value in the metadata.

Source

Thrown at pkl-core/src/main/java/org/pkl/core/packages/DependencyMetadata.java:253

          }
          return new PObject(classInfo, properties);
        }
        case "Pattern" -> {
          var value = jsObj.getString("value");
          return Pattern.compile(value);
        }
        case "DataSize" -> {
          var symbol = jsObj.getString("unit");
          var value = jsObj.get("value");
          if (value == null) {
            throw new MissingFieldException(jsObj, "value");
          }
          var unit = DataSizeUnit.parse(symbol);
          if (unit == null) {
            throw new PklException("Invalid DataSize unit symbol: " + symbol);
          }
          if (!(value instanceof Double num)) {
            throw new FormatException("double", value.getClass());
          }
          return new DataSize(num, unit);
        }
        case "Duration" -> {
          var symbol = jsObj.getString("unit");
          var value = jsObj.get("value");
          if (value == null) {
            throw new MissingFieldException(jsObj, "value");
          }
          var unit = DurationUnit.parse(symbol);
          if (unit == null) {
            throw new PklException("Invalid Duration unit symbol: " + symbol);
          }
          if (!(value instanceof Double num)) {
            throw new FormatException("double", value.getClass());
          }
          return new Duration(num, unit);
        }

View on GitHub (pinned to f3efcbfc9b)

Solutions

1. Write `value` as an unquoted JSON number: {"value": 10.0}.
2. Move any unit text out of the string and into the `unit` field.
3. Regenerate metadata with `pkl project package` to ensure correct typing.
4. Fix converters/tools that stringify numeric fields during serialization.

Example fix

// before
{"type": "DataSize", "unit": "mb", "value": "10"}
// after
{"type": "DataSize", "unit": "mb", "value": 10.0}

if (entry.get("type").asString().equals("DataSize")) {
  var v = entry.get("value");
  if (v == null || !v.isNumber()) throw new IllegalStateException("DataSize 'value' must be a JSON number, got: " + v);
}

When it happens

Trigger: Parsing metadata with a DataSize entry such as {"type": "DataSize", "unit": "mb", "value": "10"} — value is a string rather than a JSON number.

Common situations: Hand-writing annotations and quoting the number; custom generators serializing sizes as formatted strings like "10.5mb"; YAML-to-JSON conversions turning numbers into strings.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• value
• Invalid DataSize unit symbol:
• object
• array
• Could not read annotation. Invalid object:

AI-assisted analysis of apple/pkl@f3efcbfc9b (2026-09-08). Data as JSON: /api/errors/6f512738e76c1772. Report an issue: GitHub.