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1-80 SOMobjects Base Toolkit: Programmer’s Reference Manual

somFindMethod, somFindMethodOk Methods

Purpose

Finds the method procedure for a method and indicates whether it represents a static

method or a dynamic method. Not generally overridden.

IDL Syntax

boolean somFindMethod (

in somId methodId,

out somMethodPtr m);

boolean somFindMethodOk (

in somId methodId,

out somMethodPtr m);

Note: For backward compatibility, these methods do not take an Environment parameter.

Description

The somFindMethod and somFindMethodOk methods perform name-lookup method

resolution, determine the method procedure appropriate for performing the indicated

method on instances of the receiving class, and load m with the method procedure address.

For static methods, method procedure resolution is done using the instance method table of

the receiving class.

Name-lookup resolution must be used to invoke dynamic methods. Also, name-lookup can

be useful when different classes introduce methods of the same name, signature, and

desired semantics, but it is not known until runtime which of these classes should be used

as a type for the objects on which the method is to be invoked. If the signature of a method

is an unknown, then method procedures cannot be be used directly, and the somDispatch

method to be used after dynamically discovering the signature to allow the correct

arguments can be placed on a va_list.

As with any methods that return procedure pointers, these methods allow repeated

invocations of the same method procedure to be programmed. If this is done, it is up to the

programmer to prevent runtime errors by assuring that each invocation is performed either

on an instance of the class used to resolve the method procedure or of some class derived

from it. Whenever using SOM method procedure pointers, it is necessary to indicate the

arguments to be passed and the use of system linkage to the compiler, so it can generate a

correct procedure call. The way this is done depends on the compiler and the system being

used. However, C and C++ usage bindings provide an appropriate typedef for static

methods. The name of the typedef is based on the name of the class that introduces the

method, as illustrated in the following example.

Unlike the somFindMethod method, if the class does not support the specified method, the

somFindMethodOk method raises an error and halts execution.

If the class does not support the specified method, then *m is set to NULL and the return

value is meaningless. Otherwise, the returned result is true if the indicated method was a

static method.

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