The program contains a predefinition of a function, but not its actual definition.
#2509 Compile-time warning
The program contains a predefinition of a function, but not its actual definition.
Additional Information
The function 'X' was first predefined on line N of file 'F'.
or
The conversion function was first predefined on line N of file 'F'.
in case the function was predefined with define conversion-function.
Recovery
Compilation continues normally.
Explanation
A function has been predefined using elsewhere syntax, but its actual definition is missing. This message is only a warning because the function is never called.