【go語言 基礎系列】內建函式
阿新 • • 發佈：2018-11-20
原始檔builtin.go檔案中一共定義了15個內建函式，go1.9.2 版本。通過函式名可以直接呼叫函式。
- func append(slice []Type, elems ...Type) []Type
- func copy(dst, src []Type) int
- func delete(m map[Type]Type1, key Type)
- func len(v Type) int
- func cap(v Type) int
- func make(t Type, size ...IntegerType) Type
- func new(Type) *Type
- func complex(r, i FloatType) ComplexType
- func real(c ComplexType) FloatType
- func imag(c ComplexType) FloatType
- func close(c chan<- Type)
- func panic(v interface{})
- func recover() interface{}
- func print(args ...Type)
- func println(args ...Type)
【append】
將資料追加到slice的末尾，返回一個slice
125 // The append built-in function appends elements to the end of a slice. If 126 // it has sufficient capacity, the destination is resliced to accommodate the 127 // new elements. If it does not, a new underlying array will be allocated. 128 // Append returns the updated slice. It is therefore necessary to store the 129 // result of append, often in the variable holding the slice itself: 130 // slice = append(slice, elem1, elem2) 131 // slice = append(slice, anotherSlice...) 132 // As a special case, it is legal to append a string to a byte slice, like this: 133 // slice = append([]byte("hello "), "world"...) 134 func append(slice []Type, elems ...Type) []Type
函式呼叫demo
package main
import (
"fmt"
)
func main() {
var a []string
b := append(a, "x")
fmt.Println(b)
c := append(b, "y")
fmt.Println(c)
d := append(c, "z", "X", "Y", "Z")
fmt.Println(d)
fmt.Println(a, b, c, d)
str := append([]byte("hello "), "world"...)
fmt.Println(str)
fmt.Printf("%s", str)
}
【copy】
copy把源slice的資料複製到目的slice中，當目的slice的空不夠的時候會捨棄超出的部分，返回的是複製成功的元素個數
136 // The copy built-in function copies elements from a source slice into a
137 // destination slice. (As a special case, it also will copy bytes from a
138 // string to a slice of bytes.) The source and destination may overlap. Copy
139 // returns the number of elements copied, which will be the minimum of
140 // len(src) and len(dst).
141 func copy(dst, src []Type) int
函式呼叫demo
package main
import (
"fmt"
)
func main() {
strs := []string{"a", "b", "c", "d"}
strd := []string{"A", "B", "C"}
fmt.Println("before")
fmt.Println("strs is:", strs)
fmt.Println("strd is:", strd)
n := copy(strd, strs)
fmt.Println("after copy(strd,strs):")
fmt.Println("strs is:", strs)
fmt.Println("strd is:", strd)
fmt.Println("n is:", n)
var str1 []string
var str2 []string
str1 = []string{"aa", "bb", "cc", "dd", "ee"}
m := copy(str2, str1)
fmt.Println("m is:", m)
fmt.Println("str2 is:", str2)
str3 := make([]string, 3)
m2 := copy(str3, str1)
fmt.Println("m2 is:", m2)
fmt.Println("str3 is:", str3)
}
執行結果
before
strs is: [a b c d]
strd is: [A B C]
after copy(strd,strs):
strs is: [a b c d]
strd is: [a b c]
n is: 3
m is: 0
str2 is: []
m2 is: 3
str3 is: [aa bb cc]
【delete】
delete函式用於刪除map中對應key的value。
143 // The delete built-in function deletes the element with the specified key
144 // (m[key]) from the map. If m is nil or there is no such element, delete
145 // is a no-op.
146 func delete(m map[Type]Type1, key Type)
函式呼叫demo
package main
import (
"fmt"
)
func main() {
var mp = map[string]int{
"a": 1,
"b": 2,
"c": 3,
}
fmt.Println(mp)
delete(mp, "b")
fmt.Println(mp)
delete(mp, "e")
fmt.Println(mp)
}
【len】
陣列，slice map string channel等型別的長度如下面demo
148 // The len built-in function returns the length of v, according to its type:
149 // Array: the number of elements in v.
150 // Pointer to array: the number of elements in *v (even if v is nil).
151 // Slice, or map: the number of elements in v; if v is nil, len(v) is zero.
152 // String: the number of bytes in v.
153 // Channel: the number of elements queued (unread) in the channel buffer;
154 // if v is nil, len(v) is zero.
155 func len(v Type) int
函式呼叫demo
package main
import (
"fmt"
)
func main() {
arrint := []int{11, 22, 33}
arrstr := []string{"aa", "bb", "cc", "11"}
fmt.Println("len(arrint) is:", len(arrint))
fmt.Println("len(arrstr) is:", len(arrstr))
str := "abcde"
fmt.Println("len(str) is:", len(str))
var ch = make(chan int, 5)
ch <- 1
ch <- 2
fmt.Println("len(ch) is:", len(ch))
var mp map[string]int = map[string]int{
"a": 1,
"b": 2,
"c": 3,
}
fmt.Println("len(mp) is:", len(mp))
}
執行結果如下
len(arrint) is: 3
len(arrstr) is: 4
len(str) is: 5
len(ch) is: 2
len(mp) is: 3
【cap】
cap()計算 陣列 slice channel 型別的容量。沒有map
157 // The cap built-in function returns the capacity of v, according to its type:
158 // Array: the number of elements in v (same as len(v)).
159 // Pointer to array: the number of elements in *v (same as len(v)).
160 // Slice: the maximum length the slice can reach when resliced;
161 // if v is nil, cap(v) is zero.
162 // Channel: the channel buffer capacity, in units of elements;
163 // if v is nil, cap(v) is zero.
164 func cap(v Type) int
函式呼叫demo
package main
import (
"fmt"
)
func main() {
var arr [10]string = [10]string{"a", "b", "c"}
fmt.Println("arr is:", arr, "cap(arr) is:", cap(arr))
var slice []string = []string{"a", "b", "c"}
fmt.Println("slice is:", slice, "cap(slice) is:", cap(slice))
var ch = make(chan int, 10)
ch <- 1
ch <- 2
fmt.Println("cap(ch) is:", cap(ch))
}
執行結果
arr is: [a b c ] cap(arr) is: 10
slice is: [a b c] cap(slice) is: 3
cap(ch) is: 10
【make】
make()給slice map channel 分配容量空間，其中slice 可以指定長度，map無效。map的空間一般與系統記憶體有關。
166 // The make built-in function allocates and initializes an object of type
167 // slice, map, or chan (only). Like new, the first argument is a type, not a
168 // value. Unlike new, make's return type is the same as the type of its
169 // argument, not a pointer to it. The specification of the result depends on
170 // the type:
171 // Slice: The size specifies the length. The capacity of the slice is
172 // equal to its length. A second integer argument may be provided to
173 // specify a different capacity; it must be no smaller than the
174 // length, so make([]int, 0, 10) allocates a slice of length 0 and
175 // capacity 10.
176 // Map: An empty map is allocated with enough space to hold the
177 // specified number of elements. The size may be omitted, in which case
178 // a small starting size is allocated.
179 // Channel: The channel's buffer is initialized with the specified
180 // buffer capacity. If zero, or the size is omitted, the channel is
181 // unbuffered.
182 func make(t Type, size ...IntegerType) Type
函式呼叫demo
package main
import (
"fmt"
)
func main() {
var slice1 = make([]string, 0, 10)
var slice2 = make([]string, 5, 10)
fmt.Println("len(slice1) is", len(slice1), "cap(slice1) is:", cap(slice1))
fmt.Println("len(slice2) is", len(slice2), "cap(slice2) is:", cap(slice2))
var mp = make(map[string]int)
fmt.Println("len(mp) is:", len(mp))
var ch1 = make(chan int)
var ch2 = make(chan int, 10)
fmt.Println("len(ch1) is:", len(ch1), "cap(ch1) is", cap(ch1))
fmt.Println("len(ch2) is:", len(ch2), "cap(ch2) is", cap(ch2))
ch2 <- 11
ch2 <- 22
fmt.Println("len(ch1) is:", len(ch1), "cap(ch1) is", cap(ch1))
fmt.Println("len(ch2) is:", len(ch2), "cap(ch2) is", cap(ch2))
}
執行結果
len(slice1) is 0 cap(slice1) is: 10
len(slice2) is 5 cap(slice2) is: 10
len(mp) is: 0
len(ch1) is: 0 cap(ch1) is 0
len(ch2) is: 0 cap(ch2) is 10
len(ch1) is: 0 cap(ch1) is 0
len(ch2) is: 2 cap(ch2) is 10
【new】
new()返回的是對應型別的指標
184 // The new built-in function allocates memory. The first argument is a type,
185 // not a value, and the value returned is a pointer to a newly
186 // allocated zero value of that type.
187 func new(Type) *Type
函式呼叫demo
package main
import (
"fmt"
)
func main() {
i := new(int)
s := new(string)
arr := new([5]string)
slice := new([]string)
mp := new(map[string]string)
ch := new(chan int)
fmt.Printf("i type is %T\n", i)
fmt.Printf("s type is %T,len is %v\n", s, len(*s))
fmt.Printf("arr type is %T,len is %v\n", arr, len(*arr))
fmt.Printf("slice type is %T,len is %v\n", slice, len(*slice))
fmt.Printf("mp type is %T,len is %v\n", mp, len(*mp))
fmt.Printf("ch type is %T,len is %v\n", ch, len(*ch))
}
【complex，real，imag，close 略】
【panic及recover 後續詳細講解】
【print 及println 】
239 // The print built-in function formats its arguments in an
240 // implementation-specific way and writes the result to standard error.
241 // Print is useful for bootstrapping and debugging; it is not guaranteed
242 // to stay in the language.
243 func print(args ...Type)
244
245 // The println built-in function formats its arguments in an
246 // implementation-specific way and writes the result to standard error.
247 // Spaces are always added between arguments and a newline is appended.
248 // Println is useful for bootstrapping and debugging; it is not guaranteed
249 // to stay in the language.
250 func println(args ...Type)