n, err = C.sqrt(-1)
	_, err := C.voidFunc()
	var n, err = C.sqrt(1)

Calling C function pointers is currently not supported, however you can
declare Go variables which hold C function pointers and pass them
back and forth between Go and C. C code may call function pointers
received from Go. For example:

	package main

	// typedef int (*intFunc) ();
	//
	// int
	// bridge_int_func(intFunc f)

<p>
yields a function value representing <code>Mv</code> with signature
</p>

<pre>
func(tv *T, a int) int
</pre>

<p>
Such a function indirects through the receiver to create a value
to pass as the receiver to the underlying method;
the method does not overwrite the value whose address is passed in
the function call.
</p>

<p>
The final case, a value-receiver function for a pointer-receiver method,

}

// A Header represents a single header in a tar archive.
// Some fields may not be populated.
//
// For forward compatibility, users that retrieve a Header from Reader.Next,
// mutate it in some ways, and then pass it back to Writer.WriteHeader
// should do so by creating a new Header and copying the fields
// that they are interested in preserving.
type Header struct {
	// Typeflag is the type of header entry.

	type span struct {
		start int
		end   int
	}
	spans := make([]span, 0, 32)

	// Find the field start and end indices.
	// Doing this in a separate pass (rather than slicing the string s
	// and collecting the result substrings right away) is significantly
	// more efficient, possibly due to cache effects.
	start := -1 // valid span start if >= 0
	for i := 0; i < len(s); {

<p>
yields a function value representing <code>Mv</code> with signature
</p>

<pre>
func(tv *T, a int) int
</pre>

<p>
Such a function indirects through the receiver to create a value
to pass as the receiver to the underlying method;
the method does not overwrite the value whose address is passed in
the function call.
</p>

<p>
The final case, a value-receiver function for a pointer-receiver method,