If the Delphi compiler throws a Source: "W1025 Unsupported language feature: 'operator explicit'" at you, then it is likely that you forgot this, as per Uwe Raabe:
In the project options set “C/C++ Output file generation” to “Generate DCUs only” to get rid of the warning.
Via: [WayBack] Delphi Community Edition Rant. Just installed Delphi CE from the 3rd attempt. Two times I tried to install all features – both times the installer fell… – Sergey Kasandrov – Google+
Note that the documentation still indicates that W1025 has been documented since at least Delphi 2007 ([WayBack] x1025: Unsupported language feature: ‘%s’) as a C++ header translation issue, and still is ([WayBack] X1025 Unsupported language feature: ‘%s’ (Delphi) – RAD Studio), despite other causes (like "W1025 Unsupported language feature: 'custom attribute'") fail if you have only installed the Delphi personality.
–jeroen