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OptDouble

function OptDouble(const aName: String;
  const aDefault: Double): Double;

Example​

procedure ScriptEvent(var Value: variant);
var
  Payload: TJSONObject;
begin
  Payload := TJSONObject.CreateFromString('{"amount":12.5}');
  try
    Value := Payload.OptDouble('amount', 0.0);
  finally
    Payload.Free;
  end;
end;

Usage​

OptDouble converts a present non-null field with locale-sensitive StrToFloat and uses the required default only for absence or null.

Additional Technical Info​

OptDouble uses side-effect-free, case-insensitive first-match lookup. The required aDefault is returned only when the field is absent or its node is null.

A present node is converted through TJSONValue.AsDouble, which calls Delphi StrToFloat(value.AsString) with process FormatSettings. Standards-compliant dot-decimal JSON can therefore fail under a decimal-comma locale. Invalid or incompatible text raises EConvertError; it is not replaced by the default.

The method can return NaN or infinity if the underlying Delphi converter/node contains one, although RFC 8259 does not permit those JSON numbers. Duplicate names select the first physical value, and no missing field is inserted.

External references

Created 2026-07-20