Go Up to Error and Warning Messages (Delphi)
Identifier
The identifier for the $WARN directive: IMPLICIT_STRING_CAST
Description
Emitted when the compiler detects a case where it must implicitly convert an AnsiString (or AnsiChar) to some form of Unicode (a UnicodeString or a WideString). This warning is on by default.
To avoid this warning, you need to explicitly typecast your AnsiString to the new string type (UnicodeString), as follows:
<your_target_string>Β := string(<your_ansi_source);
The warning is also given for assigning a UTF8String value to an instance of UnicodeString or WideString, in which case you can use an explicit cast to UTF8String.