g_value_peek_pointer weirdness

[Sheldon Simms <wsxyz6294 yahoo com>]

I'm reading code from glib 2.3.1
In gvalue.c there are the following two functions:

158 gboolean
159 g_value_fits_pointer (const GValue *value)
160 {
161   GTypeValueTable *value_table;
162 
163   g_return_val_if_fail (G_IS_VALUE (value),
FALSE);
164 
165   value_table = g_type_value_table_peek
(G_VALUE_TYPE (value));
166 
167   return value_table->value_peek_pointer != NULL;
168 }
169 
170 gpointer
171 g_value_peek_pointer (const GValue *value)
172 {
173   GTypeValueTable *value_table;
174 
175   g_return_val_if_fail (G_IS_VALUE (value), NULL);
176 
177   value_table = g_type_value_table_peek
(G_VALUE_TYPE (value));
178   if (!value_table->value_peek_pointer)
179     g_return_val_if_fail (g_value_fits_pointer
(value) == TRUE, NULL);
180 
181   return value_table->value_peek_pointer (value);
182 }

It seems to me that lines 178 and 179 are wrong. If
there is no function
value_peek_pointer for this value type, then how does
it help anything if
g_value_fits_pointer() were to return TRUE?
value_peek_pointer would still
be a null pointer and cause a crash at line 181.

Of course, I know that value_peek_pointer would still
be a null pointer
primarily because I can see the implementation of
g_value_fits_pointer().
However, even if I didn't know the implementation of
g_value_fits_pointer(),
it is not reasonable to assume that
g_value_fits_pointer() would fill
value_peek_pointer with a valid pointer. Why would a
predicate do that?
And how would it know what function's address should
go there? It doesn't
have any more information than g_value_peek_pointer()
does.

Since I do know know the implementation of
g_value_fits_pointer(), however,
I know that everything will be ok; because when
value_peek_pointer is a null
pointer, g_value_fits_pointer() always return FALSE,
and cause
g_value_peek_pointer() to return NULL. But in that
case, why not just do
this:

178   if (!value_table->value_peek_pointer)
179     return NULL;
180 
181   return value_table->value_peek_pointer (value);

-Sheldon


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