the memory occupied by the field, not the entire struct. When passing a
pointer to an element in an array or slice, the Go memory in question is
the entire array or the entire backing array of the slice.

C code may keep a copy of a Go pointer only as long as the memory it
points to is pinned.

C code may not keep a copy of a Go pointer after the call returns,

line := Line{origin, Point3D{y: -4, z: 12.3}}  // zero value for line.q.x
</pre>

<p>
For array and slice literals the following rules apply:
</p>
<ul>
	<li>Each element has an associated integer index marking
	    its position in the array.
	</li>
	<li>An element with a key uses the key as its index. The
	    key must be a non-negative constant
	    <a href="#Representability">representable</a> by

		}

		if cap(input) != 0 && unsafe.SliceData(input) == unsafe.SliceData(clone) {
			t.Errorf("Clone(%q) return value should not reference inputs backing memory.", input)
		}
	}

	if !p.more() {
		return EOF
	}
	tok := p.input[p.inputPos]
	p.inputPos++
	return tok
}

func (p *Parser) back() {
	if p.inputPos == 0 {
		p.errorf("internal error: backing up before BOL")
	} else {
		p.inputPos--
	}
}

func (p *Parser) peek() lex.ScanToken {
	if p.more() {
		return p.input[p.inputPos].ScanToken
	}
	return scanner.EOF
}

line := Line{origin, Point3D{y: -4, z: 12.3}}  // zero value for line.q.x
</pre>

<p>
For array and slice literals the following rules apply:
</p>
<ul>
	<li>Each element has an associated integer index marking
	    its position in the array.
	</li>
	<li>An element with a key uses the key as its index. The
	    key must be a non-negative constant
	    <a href="#Representability">representable</a> by

*p /= 2
*p += i
</pre>

<p>
If <code>i</code> and <code>*p</code> start equal to 2,
the original code does <code>*p = 3</code>,
so a racing thread can read only 2 or 3 from <code>*p</code>.
The rewritten code does <code>*p = 1</code> and then <code>*p = 3</code>,
allowing a racing thread to read 1 as well.
</p>

<p>
Note that all these optimizations are permitted in C/C++ compilers: