# Source file src/builtin/builtin.go

1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 /* 6 Package builtin provides documentation for Go's predeclared identifiers. 7 The items documented here are not actually in package builtin 8 but their descriptions here allow godoc to present documentation 9 for the language's special identifiers. 10 */ 11 package builtin 12 13 import "cmp" 14 15 // bool is the set of boolean values, true and false. 16 type bool bool 17 18 // true and false are the two untyped boolean values. 19 const ( 20 true = 0 == 0 // Untyped bool. 21 false = 0 != 0 // Untyped bool. 22 ) 23 24 // uint8 is the set of all unsigned 8-bit integers. 25 // Range: 0 through 255. 26 type uint8 uint8 27 28 // uint16 is the set of all unsigned 16-bit integers. 29 // Range: 0 through 65535. 30 type uint16 uint16 31 32 // uint32 is the set of all unsigned 32-bit integers. 33 // Range: 0 through 4294967295. 34 type uint32 uint32 35 36 // uint64 is the set of all unsigned 64-bit integers. 37 // Range: 0 through 18446744073709551615. 38 type uint64 uint64 39 40 // int8 is the set of all signed 8-bit integers. 41 // Range: -128 through 127. 42 type int8 int8 43 44 // int16 is the set of all signed 16-bit integers. 45 // Range: -32768 through 32767. 46 type int16 int16 47 48 // int32 is the set of all signed 32-bit integers. 49 // Range: -2147483648 through 2147483647. 50 type int32 int32 51 52 // int64 is the set of all signed 64-bit integers. 53 // Range: -9223372036854775808 through 9223372036854775807. 54 type int64 int64 55 56 // float32 is the set of all IEEE-754 32-bit floating-point numbers. 57 type float32 float32 58 59 // float64 is the set of all IEEE-754 64-bit floating-point numbers. 60 type float64 float64 61 62 // complex64 is the set of all complex numbers with float32 real and 63 // imaginary parts. 64 type complex64 complex64 65 66 // complex128 is the set of all complex numbers with float64 real and 67 // imaginary parts. 68 type complex128 complex128 69 70 // string is the set of all strings of 8-bit bytes, conventionally but not 71 // necessarily representing UTF-8-encoded text. A string may be empty, but 72 // not nil. Values of string type are immutable. 73 type string string 74 75 // int is a signed integer type that is at least 32 bits in size. It is a 76 // distinct type, however, and not an alias for, say, int32. 77 type int int 78 79 // uint is an unsigned integer type that is at least 32 bits in size. It is a 80 // distinct type, however, and not an alias for, say, uint32. 81 type uint uint 82 83 // uintptr is an integer type that is large enough to hold the bit pattern of 84 // any pointer. 85 type uintptr uintptr 86 87 // byte is an alias for uint8 and is equivalent to uint8 in all ways. It is 88 // used, by convention, to distinguish byte values from 8-bit unsigned 89 // integer values. 90 type byte = uint8 91 92 // rune is an alias for int32 and is equivalent to int32 in all ways. It is 93 // used, by convention, to distinguish character values from integer values. 94 type rune = int32 95 96 // any is an alias for interface{} and is equivalent to interface{} in all ways. 97 type any = interface{} 98 99 // comparable is an interface that is implemented by all comparable types 100 // (booleans, numbers, strings, pointers, channels, arrays of comparable types, 101 // structs whose fields are all comparable types). 102 // The comparable interface may only be used as a type parameter constraint, 103 // not as the type of a variable. 104 type comparable interface{ comparable } 105 106 // iota is a predeclared identifier representing the untyped integer ordinal 107 // number of the current const specification in a (usually parenthesized) 108 // const declaration. It is zero-indexed. 109 const iota = 0 // Untyped int. 110 111 // nil is a predeclared identifier representing the zero value for a 112 // pointer, channel, func, interface, map, or slice type. 113 var nil Type // Type must be a pointer, channel, func, interface, map, or slice type 114 115 // Type is here for the purposes of documentation only. It is a stand-in 116 // for any Go type, but represents the same type for any given function 117 // invocation. 118 type Type int 119 120 // Type1 is here for the purposes of documentation only. It is a stand-in 121 // for any Go type, but represents the same type for any given function 122 // invocation. 123 type Type1 int 124 125 // IntegerType is here for the purposes of documentation only. It is a stand-in 126 // for any integer type: int, uint, int8 etc. 127 type IntegerType int 128 129 // FloatType is here for the purposes of documentation only. It is a stand-in 130 // for either float type: float32 or float64. 131 type FloatType float32 132 133 // ComplexType is here for the purposes of documentation only. It is a 134 // stand-in for either complex type: complex64 or complex128. 135 type ComplexType complex64 136 137 // The append built-in function appends elements to the end of a slice. If 138 // it has sufficient capacity, the destination is resliced to accommodate the 139 // new elements. If it does not, a new underlying array will be allocated. 140 // Append returns the updated slice. It is therefore necessary to store the 141 // result of append, often in the variable holding the slice itself: 142 // 143 // slice = append(slice, elem1, elem2) 144 // slice = append(slice, anotherSlice...) 145 // 146 // As a special case, it is legal to append a string to a byte slice, like this: 147 // 148 // slice = append([]byte("hello "), "world"...) 149 func append(slice []Type, elems ...Type) []Type 150 151 // The copy built-in function copies elements from a source slice into a 152 // destination slice. (As a special case, it also will copy bytes from a 153 // string to a slice of bytes.) The source and destination may overlap. Copy 154 // returns the number of elements copied, which will be the minimum of 155 // len(src) and len(dst). 156 func copy(dst, src []Type) int 157 158 // The delete built-in function deletes the element with the specified key 159 // (m[key]) from the map. If m is nil or there is no such element, delete 160 // is a no-op. 161 func delete(m map[Type]Type1, key Type) 162 163 // The len built-in function returns the length of v, according to its type: 164 // 165 // Array: the number of elements in v. 166 // Pointer to array: the number of elements in *v (even if v is nil). 167 // Slice, or map: the number of elements in v; if v is nil, len(v) is zero. 168 // String: the number of bytes in v. 169 // Channel: the number of elements queued (unread) in the channel buffer; 170 // if v is nil, len(v) is zero. 171 // 172 // For some arguments, such as a string literal or a simple array expression, the 173 // result can be a constant. See the Go language specification's "Length and 174 // capacity" section for details. 175 func len(v Type) int 176 177 // The cap built-in function returns the capacity of v, according to its type: 178 // 179 // Array: the number of elements in v (same as len(v)). 180 // Pointer to array: the number of elements in *v (same as len(v)). 181 // Slice: the maximum length the slice can reach when resliced; 182 // if v is nil, cap(v) is zero. 183 // Channel: the channel buffer capacity, in units of elements; 184 // if v is nil, cap(v) is zero. 185 // 186 // For some arguments, such as a simple array expression, the result can be a 187 // constant. See the Go language specification's "Length and capacity" section for 188 // details. 189 func cap(v Type) int 190 191 // The make built-in function allocates and initializes an object of type 192 // slice, map, or chan (only). Like new, the first argument is a type, not a 193 // value. Unlike new, make's return type is the same as the type of its 194 // argument, not a pointer to it. The specification of the result depends on 195 // the type: 196 // 197 // Slice: The size specifies the length. The capacity of the slice is 198 // equal to its length. A second integer argument may be provided to 199 // specify a different capacity; it must be no smaller than the 200 // length. For example, make([]int, 0, 10) allocates an underlying array 201 // of size 10 and returns a slice of length 0 and capacity 10 that is 202 // backed by this underlying array. 203 // Map: An empty map is allocated with enough space to hold the 204 // specified number of elements. The size may be omitted, in which case 205 // a small starting size is allocated. 206 // Channel: The channel's buffer is initialized with the specified 207 // buffer capacity. If zero, or the size is omitted, the channel is 208 // unbuffered. 209 func make(t Type, size ...IntegerType) Type 210 211 // The max built-in function returns the largest value of a fixed number of 212 // arguments of [cmp.Ordered] types. There must be at least one argument. 213 // If T is a floating-point type and any of the arguments are NaNs, 214 // max will return NaN. 215 func max[T cmp.Ordered](x T, y ...T) T 216 217 // The min built-in function returns the smallest value of a fixed number of 218 // arguments of [cmp.Ordered] types. There must be at least one argument. 219 // If T is a floating-point type and any of the arguments are NaNs, 220 // min will return NaN. 221 func min[T cmp.Ordered](x T, y ...T) T 222 223 // The new built-in function allocates memory. The first argument is a type, 224 // not a value, and the value returned is a pointer to a newly 225 // allocated zero value of that type. 226 func new(Type) *Type 227 228 // The complex built-in function constructs a complex value from two 229 // floating-point values. The real and imaginary parts must be of the same 230 // size, either float32 or float64 (or assignable to them), and the return 231 // value will be the corresponding complex type (complex64 for float32, 232 // complex128 for float64). 233 func complex(r, i FloatType) ComplexType 234 235 // The real built-in function returns the real part of the complex number c. 236 // The return value will be floating point type corresponding to the type of c. 237 func real(c ComplexType) FloatType 238 239 // The imag built-in function returns the imaginary part of the complex 240 // number c. The return value will be floating point type corresponding to 241 // the type of c. 242 func imag(c ComplexType) FloatType 243 244 // The clear built-in function clears maps and slices. 245 // For maps, clear deletes all entries, resulting in an empty map. 246 // For slices, clear sets all elements up to the length of the slice 247 // to the zero value of the respective element type. If the argument 248 // type is a type parameter, the type parameter's type set must 249 // contain only map or slice types, and clear performs the operation 250 // implied by the type argument. 251 func clear[T ~[]Type | ~map[Type]Type1](t T) 252 253 // The close built-in function closes a channel, which must be either 254 // bidirectional or send-only. It should be executed only by the sender, 255 // never the receiver, and has the effect of shutting down the channel after 256 // the last sent value is received. After the last value has been received 257 // from a closed channel c, any receive from c will succeed without 258 // blocking, returning the zero value for the channel element. The form 259 // 260 // x, ok := <-c 261 // 262 // will also set ok to false for a closed and empty channel. 263 func close(c chan<- Type) 264 265 // The panic built-in function stops normal execution of the current 266 // goroutine. When a function F calls panic, normal execution of F stops 267 // immediately. Any functions whose execution was deferred by F are run in 268 // the usual way, and then F returns to its caller. To the caller G, the 269 // invocation of F then behaves like a call to panic, terminating G's 270 // execution and running any deferred functions. This continues until all 271 // functions in the executing goroutine have stopped, in reverse order. At 272 // that point, the program is terminated with a non-zero exit code. This 273 // termination sequence is called panicking and can be controlled by the 274 // built-in function recover. 275 // 276 // Starting in Go 1.21, calling panic with a nil interface value or an 277 // untyped nil causes a run-time error (a different panic). 278 // The GODEBUG setting panicnil=1 disables the run-time error. 279 func panic(v any) 280 281 // The recover built-in function allows a program to manage behavior of a 282 // panicking goroutine. Executing a call to recover inside a deferred 283 // function (but not any function called by it) stops the panicking sequence 284 // by restoring normal execution and retrieves the error value passed to the 285 // call of panic. If recover is called outside the deferred function it will 286 // not stop a panicking sequence. In this case, or when the goroutine is not 287 // panicking, or if the argument supplied to panic was nil, recover returns 288 // nil. Thus the return value from recover reports whether the goroutine is 289 // panicking. 290 func recover() any 291 292 // The print built-in function formats its arguments in an 293 // implementation-specific way and writes the result to standard error. 294 // Print is useful for bootstrapping and debugging; it is not guaranteed 295 // to stay in the language. 296 func print(args ...Type) 297 298 // The println built-in function formats its arguments in an 299 // implementation-specific way and writes the result to standard error. 300 // Spaces are always added between arguments and a newline is appended. 301 // Println is useful for bootstrapping and debugging; it is not guaranteed 302 // to stay in the language. 303 func println(args ...Type) 304 305 // The error built-in interface type is the conventional interface for 306 // representing an error condition, with the nil value representing no error. 307 type error interface { 308 Error() string 309 } 310