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TJSONDouble

TJSONDouble = class(TJSONNumber)

Example​

procedure ScriptEvent(var Value: variant);
var
  Document: TJSONObject;
begin
  Document := TJSONObject.Create;
  try
    Document.AddDouble('amount', 12.5);
    Value := Document.AsString;  // Formatting uses process settings.
  finally
    Document.Free;
  end;
end;

Usage​

TJSONDouble represents a mutable binary64 JSON number whose text conversion is locale-sensitive and limited to 15 significant digits.

Additional Technical Info​

The native TJSONDouble class stores a Delphi Double; correctly constructed helper/parser nodes have ValueType = jsNumber. Its native TJSONNumber ancestor descends from TJSONValue, is hidden and adds no fields or methods.

The PascalScript compiler registration does not reproduce that native inheritance: it registers hidden TJSONNumber directly beneath TObject, then registers TJSONDouble beneath it. A TJSONDouble-typed script expression consequently exposes only Value and the TObject surface. It cannot call TJSONValue members such as AsString, IsNull, Clear, CopyFrom or IsEqual, and it is not compile-time assignable to TJSONValue.

This also changes direct construction. TJSONDouble.Create resolves through PascalScript's TObject.Create, not the registered virtual TJSONValue.Create, so it allocates the native object without running the JSON value-type initializer. Its Value field works, but do not treat that directly constructed instance as a correctly initialized JSON node or attempt to insert it into a tree. Prefer native helper/parser construction, as in the example. A helper-created node is owned by its parent.

Conversion contract​

When native JSON code serializes a correctly initialized node—or when it is accessed through a base-typed TJSONValue reference—AsString calls Delphi FloatToStr with the process FormatSettings. In the installed Studio 37 implementation this uses general formatting with 15 significant digits. It does not use a JSON-invariant decimal point, so a decimal-comma locale can emit text such as 12,5; when inserted unquoted into an object or array, that is not the intended JSON number and can change the apparent structure.

Native/base-typed AsString assignment calls locale-sensitive StrToFloat, then stores the result as a Double. Surrounding blanks may be accepted by the Delphi converter, exponent notation is accepted and invalid text raises EConvertError. Because the override clears null state before conversion, a failed assignment leaves the prior numeric payload but makes the node non-null. This member is not exposed through a TJSONDouble-typed script variable because of the compiler hierarchy defect.

This differs from the Deltics JSON reader: the reader chooses TJSONDouble only when the source token contains a period. An exponent-only token such as 1e3 is routed to TJSONInteger and then fails, even though direct TJSONDouble.AsString := '1e3' is convertible.

Double can represent NaN and infinities, and Value does not reject them. RFC 8259 does not permit those values as JSON numbers. General formatting can also lose low-order binary64 precision because it is limited to 15 significant digits. Treat generated text as an interoperability boundary, not a lossless round trip.

Null and base-typed behavior​

Native Clear, or a call through a TJSONValue-typed reference, marks a correctly initialized node null but retains the stored Double; reading Value through a valid class view still returns it. Objects serialize that state as null. Arrays instead receive blank AsString for the jsNumber node, creating an empty token or collapsing a one-item array to [].

When the instance is reached through a TJSONValue reference, that type's script NotNull property remains incorrectly wired to IsNull. Native TJSONDouble.CopyFrom assumes another exact TJSONDouble without a runtime guard, and native IsEqual compares formatted AsString; neither member is available through a TJSONDouble-typed script expression. Values that format identically at 15 digits can therefore compare equal through the base API even when their stored binary64 payloads differ.

External references

Created 2026-07-20