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Inside Macintosh: Operating System Utilities /

Chapter 1 - Gestalt Manager / Gestalt Manager Reference

Gestalt Manager Routines / Modifying a Selector Function

ReplaceGestalt

You can use the ReplaceGestalt function to replace the function that is currently associated with a selector.

FUNCTION ReplaceGestalt (selector: OSType; 
                         gestaltFunction: SelectorFunctionUUP;
                         VAR oldGestaltFunction:
                         SelectorFunctionUUP): OSErr;

selector

The selector code for the function being replaced.

gestaltFunction

A pointer to the new selector function.

oldGestaltFunction

On exit, a pointer to the function previously associated with the specified selector.

DESCRIPTION

The ReplaceGestalt function replaces the selector function associated with an existing selector code.

So that your function can call the function previously associated with the selector, ReplaceGestalt places the address of the old selector function in the oldGestaltFunction parameter. If ReplaceGestalt returns an error of any type, then the value of oldGestaltFunction is undefined.

SPECIAL CONSIDERATIONS

The ReplaceGestalt function might move memory and should not be called at interrupt time.

ASSEMBLY-LANGUAGE INFORMATION

The registers on entry and exit for the ReplaceGestalt function are

Registers on entry
A0	Address of new selector function
D0	Selector code

Registers on exit
A0	Address of old selector function
D0	Result code

RESULT CODES

noErr	0	No error
gestaltUndefSelectorErr	-5551	Undefined selector
gestaltLocationErr	-5553	Function not in system heap

SEE ALSO

See "Modifying a Selector Function" on page 1-13 for a discussion of replacing selector functions. See "Adding a New Selector Code" beginning on page 1-10 for a sample selector function.