called by C code may take a Go pointer but it must preserve the property
that the Go memory to which it points (and the Go memory to which that
memory points, and so on) is pinned.

These rules are checked dynamically at runtime. The checking is
controlled by the cgocheck setting of the GODEBUG environment
variable. The default setting is GODEBUG=cgocheck=1, which implements
reasonably cheap dynamic checks. These checks may be disabled

higher-dimensional objects.
With arrays of arrays, the inner arrays are, by construction, always the same length;
however with slices of slices (or arrays of slices), the inner lengths may vary dynamically.
Moreover, the inner slices must be initialized individually.
</p>

<h3 id="Struct_types">Struct types</h3>

<p>
A struct is a sequence of named elements, called fields, each of which has a

a C source file for 6c; both compile as part of the named package
(gmp, in this example).  The third, gcc.c, is a C source file for gcc;
it compiles into a shared object (.so) that is dynamically linked into
any 6.out that imports the first two files.

The stanza

	// #include <gmp.h>
	import "C"

is a signal to cgo.  The doc comment on the import of "C" provides

higher-dimensional objects.
With arrays of arrays, the inner arrays are, by construction, always the same length;
however with slices of slices (or arrays of slices), the inner lengths may vary dynamically.
Moreover, the inner slices must be initialized individually.
</p>

<h3 id="Struct_types">Struct types</h3>

<p>
A struct is a sequence of named elements, called fields, each of which has a