</p>

<pre>
v, ok = x.(T)
v, ok := x.(T)
var v, ok = x.(T)
var v, ok interface{} = x.(T) // dynamic types of v and ok are T and bool
</pre>

<p>
yields an additional untyped boolean value. The value of <code>ok</code> is <code>true</code>
if the assertion holds. Otherwise it is <code>false</code> and the value of <code>v</code> is

// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Test that it's OK to have C code that does nothing other than
// initialize a global variable.  This used to fail with gccgo.

package gcc68255

/*
#include "c.h"
*/
import "C"

func F() bool {
	return C.v != nil

// return the remainder as r.
func parsePAXRecord(s string) (k, v, r string, err error) {
	// The size field ends at the first space.
	nStr, rest, ok := strings.Cut(s, " ")
	if !ok {
		return "", "", s, ErrHeader
	}

	// Parse the first token as a decimal integer.
	n, perr := strconv.ParseInt(nStr, 10, 0) // Intentionally parse as native int

		fatal("fopen failed")
	}
	if Fgetc(f) != '/' || Fgetc(f) != '/' || Fgetc(f) != ' ' || Fgetc(f) != 'C' {
		fatal("read unexpected characters")
	}
	if Fclose(f) != 0 {
		fatal("fclose failed")
	}

	println("OK")
}

func fatal(f string, args ...any) {
	fmt.Fprintln(os.Stderr, fmt.Sprintf(f, args...))
	os.Exit(1)

	default:
		return n, nil
	}
}

func (sw *sparseFileWriter) ReadFrom(r io.Reader) (n int64, err error) {
	rs, ok := r.(io.ReadSeeker)
	if ok {
		if _, err := rs.Seek(0, io.SeekCurrent); err != nil {
			ok = false // Not all io.Seeker can really seek
		}
	}
	if !ok {
		return io.Copy(struct{ io.Writer }{sw}, r)
	}

	var readLastByte bool
	pos0 := sw.pos

	case '\u00B7': // Represents the period in runtime.exit. U+00B7 '·' middle dot
		return true
	case '\u2215': // Represents the slash in runtime/debug.setGCPercent. U+2215 '∕' division slash
		return true
	}
	// Digits are OK only after the first character.
	return i > 0 && unicode.IsDigit(ch)
}

func (t *Tokenizer) Text() string {
	switch t.tok {
	case LSH:
		return "<<"
	case RSH:
		return ">>"
	case ARR:
		return "->"

func BenchmarkReaderWriteToOptimal(b *testing.B) {
	const bufSize = 16 << 10
	buf := make([]byte, bufSize)
	r := bytes.NewReader(buf)
	srcReader := NewReaderSize(onlyReader{r}, 1<<10)
	if _, ok := io.Discard.(io.ReaderFrom); !ok {
		b.Fatal("io.Discard doesn't support ReaderFrom")
	}
	for i := 0; i < b.N; i++ {
		r.Seek(0, io.SeekStart)
		srcReader.Reset(onlyReader{r})
		n, err := srcReader.WriteTo(io.Discard)

		return nil
	}
	if cutset == "" {
		return s
	}
	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
		return trimLeftByte(trimRightByte(s, cutset[0]), cutset[0])
	}
	if as, ok := makeASCIISet(cutset); ok {
		return trimLeftASCII(trimRightASCII(s, &as), &as)
	}
	return trimLeftUnicode(trimRightUnicode(s, cutset), cutset)
}

// TrimLeft returns a subslice of s by slicing off all leading

	// EVEX: VCVTPD2DQ with Y suffix (VL=2).
	VCVTPD2DQY (BX), X20  // 62e1ff28e623
	VCVTPD2DQY (R11), X30 // 6241ff28e633
	// XED encoder uses EVEX.X=0 for these; most x86 tools use EVEX.X=1.
	// Either way is OK.
	VMOVQ SP, X20  // 62e1fd086ee4 or 62a1fd086ee4
	VMOVQ BP, X20  // 62e1fd086ee5 or 62a1fd086ee5
	VMOVQ R14, X20 // 62c1fd086ee6 or 6281fd086ee6
	// "VMOVQ r/m64, xmm1"/6E vs "VMOVQ xmm2/m64, xmm1"/7E with mem operand.

// from a closed channel c, any receive from c will succeed without
// blocking, returning the zero value for the channel element. The form
//
//	x, ok := <-c
//
// will also set ok to false for a closed and empty channel.
func close(c chan<- Type)

// The panic built-in function stops normal execution of the current