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