but that should be extremely rare.

GODEBUG settings added for compatibility will be maintained
for a minimum of two years (four Go releases).
Some, such as `http2client` and `http2server`,
will be maintained much longer, even indefinitely.

When possible, each GODEBUG setting has an associated
[runtime/metrics](/pkg/runtime/metrics/) counter
named `/godebug/non-default-behavior/<name>:events`

/*
Cgo enables the creation of Go packages that call C code.

# Using cgo with the go command

To use cgo write normal Go code that imports a pseudo-package "C".
The Go code can then refer to types such as C.size_t, variables such
as C.stdout, or functions such as C.putchar.

If the import of "C" is immediately preceded by a comment, that
comment, called the preamble, is used as a header when compiling
the C parts of the package. For example:

// that contains a zip file bigger.zip that contains a zip file
// big.zip that contains big.file, which contains 2³²-1 zeros.
// The big.zip file is interesting because it has no zip64 header,
// much like the innermost zip files in the well-known 42.zip.
//
// biggest.zip was generated by changing isZip64 to use > uint32max
// instead of >= uint32max and then running this program:
//
//	package main
//

		if c == r {
			return i
		}
	}
	// invalid: missing return statement
}
</pre>

<p>
A function declaration may omit the body. Such a declaration provides the
signature for a function implemented outside Go, such as an assembly routine.
</p>

<pre>
func min(x int, y int) int {
	if x &lt; y {
		return x
	}
	return y
}

		return 0
	}
	return uint16(reg)
}

// Note: There are two changes in the expression handling here
// compared to the old yacc/C implementations. Neither has
// much practical consequence because the expressions we
// see in assembly code are simple, but for the record:
//
// 1) Evaluation uses uint64; the old one used int64.
// 2) Precedence uses Go rules not C rules.

			// the cutover is about 16 byte skips.
			// TODO: if large prefixes of sep are matching
			// we should cutover at even larger average skips,
			// because Equal becomes that much more expensive.
			// This code does not take that effect into account.
			j := bytealg.IndexRabinKarp(s[i:], sep)
			if j < 0 {
				return -1
			}
			return i + j
		}
	}
	return -1
}

</p>


<h3 id="advice">Advice</h3>

<p>
Programs that modify data being simultaneously accessed by multiple goroutines
must serialize such access.
</p>

<p>
To serialize access, protect the data with channel operations or other synchronization primitives
such as those in the <a href="/pkg/sync/"><code>sync</code></a>
and <a href="/pkg/sync/atomic/"><code>sync/atomic</code></a> packages.
</p>

<p>

	TypeXHeader = 'x'

	// Type 'g' is used by the PAX format to store key-value records that
	// are relevant to all subsequent files.
	// This package only supports parsing and composing such headers,
	// but does not currently support persisting the global state across files.
	TypeXGlobalHeader = 'g'

	// Type 'S' indicates a sparse file in the GNU format.
	TypeGNUSparse = 'S'

A visible effect of this change is that `len` and `cap` of timer channels
now returns 0 instead of 1, which may affect programs that
poll the length to decide whether a receive on the timer channel
will succeed.
Such code should use a non-blocking receive instead.

These new behaviors are only enabled when the main Go program
is in a module with a `go.mod` `go` line using Go 1.23.0 or later.

// len(src) and len(dst).
func copy(dst, src []Type) int

// The delete built-in function deletes the element with the specified key
// (m[key]) from the map. If m is nil or there is no such element, delete
// is a no-op.
func delete(m map[Type]Type1, key Type)

// The len built-in function returns the length of v, according to its type:
//
//	Array: the number of elements in v.