No identifier may be declared twice in the same block, and
no identifier may be declared in both the file and package block.
</p>

<p>
The <a href="#Blank_identifier">blank identifier</a> may be used like any other identifier
in a declaration, but it does not introduce a binding and thus is not declared.
In the package block, the identifier <code>init</code> may only be used for

Each file is a list of API features, one per line.

go1.txt (and similarly named files) are frozen once a version has been
shipped. Each file adds new lines but does not remove any.

except.txt lists features that may disappear without breaking true
compatibility.

Starting with go1.19.txt, each API feature line must end in "#nnnnn"
giving the GitHub issue number of the proposal issue that accepted

### New unique package

The new [unique](/pkg/unique) package provides facilities for
canonicalizing values (like "interning" or "hash-consing").

Any value of comparable type may be canonicalized with the new
`Make[T]` function, which produces a reference to a canonical copy of
the value in the form of a `Handle[T]`.
Two `Handle[T]` are equal if and only if the values used to produce the
handles are equal, allowing programs to deduplicate values and reduce

// imaginary parts.
type complex128 complex128

// string is the set of all strings of 8-bit bytes, conventionally but not
// necessarily representing UTF-8-encoded text. A string may be empty, but
// not nil. Values of string type are immutable.
type string string

// int is a signed integer type that is at least 32 bits in size. It is a
// distinct type, however, and not an alias for, say, int32.

Earlier versions of Go used channels with a one-element buffer,
making it difficult to use `Reset` and `Stop` correctly.
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

	}
}

// registerList parses an ARM or ARM64 register list expression, a list of
// registers in []. There may be comma-separated ranges or individual
// registers, as in [R1,R3-R5] or [V1.S4, V2.S4, V3.S4, V4.S4].
// For ARM, only R0 through R15 may appear.
// For ARM64, V0 through V31 with arrangement may appear.
//
// For 386/AMD64 register list specifies 4VNNIW-style multi-source operand.

	return Map(c.ToTitle, s)
}

// ToValidUTF8 treats s as UTF-8-encoded bytes and returns a copy with each run of bytes
// representing invalid UTF-8 replaced with the bytes in replacement, which may be empty.
func ToValidUTF8(s, replacement []byte) []byte {
	b := make([]byte, 0, len(s)+len(replacement))
	invalid := false // previous byte was from an invalid UTF-8 sequence
	for i := 0; i < len(s); {
		c := s[i]

func (sw sparseFileWriter) logicalRemaining() int64 {
	return sw.sp[len(sw.sp)-1].endOffset() - sw.pos
}
func (sw sparseFileWriter) physicalRemaining() int64 {
	return sw.fw.physicalRemaining()
}

// zeroWriter may only be written with NULs, otherwise it returns errWriteHole.
type zeroWriter struct{}

func (zeroWriter) Write(b []byte) (int, error) {
	for i, c := range b {
		if c != 0 {
			return i, errWriteHole
		}
	}

// lines, bytes, UTF-8-encoded runes, and space-delimited words. The
// client may instead provide a custom split function.
//
// Scanning stops unrecoverably at EOF, the first I/O error, or a token too
// large to fit in the [Scanner.Buffer]. When a scan stops, the reader may have
// advanced arbitrarily far past the last token. Programs that need more

(discussed below).

When preparing any change that is permitted by Go 1 compatibility
but may nonetheless break some existing programs,
we first engineer the change to keep as many existing programs working as possible.
For the remaining programs,
we define a new GODEBUG setting that
allows individual programs to opt back in to the old behavior.
A GODEBUG setting may not be added if doing so is infeasible,
but that should be extremely rare.