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Create

constructor Create;

Example​

procedure ScriptEvent(var Value: variant);
var
  Text: TJSONString;
begin
  Text := TJSONString.Create;  // Do not call TJSONValue.Create.
  try
    Text.Value := 'ready';
    Value := Text.AsString;
  finally
    Text.Free;
  end;
end;

Usage​

Create creates an empty value for a supported JSON type. Calling it directly for TJSONValue raises an error; create the required JSON type instead.

Additional Technical Info​

Create is the virtual constructor declared by TJSONValue and inherited by correctly registered descendants. After TObject initialization it tests the actual runtime instance, in this order: array, String, Boolean, null, number, object. It stores the corresponding immutable ValueType. A raw TJSONValue or abstract raw TJSONText matches none of those classes and raises EJSONError with Unknown JSON value class.

Use a concrete public constructor such as TJSONString.Create, TJSONBoolean.Create, TJSONArray.Create or TJSONObject.Create. The returned object is caller-owned until explicitly transferred to an owning container. Free a standalone value in finally; never separately free a child already owned by an object or array. Delphi automatically destroys a failed constructor instance, so the raw-class exception does not leave that instance allocated.

Correctly constructed String, Boolean and number storage begins at the Delphi zero value and is non-null because the stored flag is initially false. Arrays and objects begin empty and always report non-null. TJSONNull always reports null. The constructor does not set Name.

The PascalScript importer has a separate numeric ancestry defect. It registers hidden TJSONNumber beneath TObject, not TJSONValue, so a direct TJSONDouble.Create or TJSONInteger.Create expression can resolve to TObject.Create and skip this classifier. Such a typed expression also lacks the common value surface. Prefer parser/helper-created numeric nodes; see the numeric class pages for the exact limitation.

Construction is synchronous. Scalar cost is constant; object and array constructors additionally allocate their owning list. Allocation errors and EJSONError propagate.

External references

Created 2026-07-15