Re: [9fans] thread

[dmr@plan9.bell-labs.com]

So far as I can determine, the Plan 9 C compiler is
conformant here.

If you have, say, an

	int A[10];

then just A is the address of A and has type int *.
&A is a pointer to this array of 10 integers; it will
have the same value, as a pointer, but a different type:

 int (*)[10]

The reason why the initialization in the thread man page,
(and presumably the code) works is that the thing being
assigned to is void *, and any object pointer will fit; the
coercion just happens.

The & in &m is redundant, probably misleading, but ultimately
harmless.  Kenji's example with print likewise has the
same character, since print is a variadic function, and all
his second arguments fall under the ... in its declaration,
and so aren't type-checked.

Incidentally, there is no C-language guarantee that the
actual bit pattern produced by A and &A will be identical,
though in practice they usually will be for most compilers,
yet they still have different types.

For a case in which the type-checking is more evident, without
the laxness of void * or ..., try compiling

#include <u.h>
#include <libc.h>

void t1(int *ip);
void t2(int (*iap)[10]);

void
main(void)
{
	int ia[10];

	t1(ia);
	t1(&ia);
	t2(ia);
	t2(&ia);
}

You will get errors on lines 13 [ t1(&ia) ] and
14 [ t2(ia) ].

	Dennis