Legacy Document

Inside Macintosh: Operating System Utilities /

Chapter 1 - Gestalt Manager / Gestalt Manager Reference

Application-Defined Routines / The Selector Function

MySelectorFunction

The selector function is responsible for placing the requested information in the response parameter and returning an appropriate error code.

FUNCTION MySelectorFunction (selector: OSType; 
                             VAR response: LongInt): OSErr;

selector

The selector code that triggers the function.

response

On exit, the information.

DESCRIPTION

The selector function places the requested information in the response parameter and returns a result code. If the information is not available, the selector function returns the appropriate error code, which Gestalt returns as its function result.

A selector function can call Gestalt or even other selector functions. It must reside in the system heap.

ASSEMBLY-LANGUAGE INFORMATION

The registers on entry and exit for the selector function are

Registers on entry
D0	Selector code

Registers on exit
A0	Response
D0	Result code

RESULT CODES

noErr	0	No error
gestaltUnknownErr	-5550	Could not obtain the response

SEE ALSO

See "Adding a New Selector Code" beginning on page 1-10 for a sample selector function and a procedure that installs it in the system heap. For information about the NewGestalt function, see page 1-34. For information about the ReplaceGestalt function, see page 1-35.