go的内置函数
go内置了一些函数，这些函数可以直接使用。
关闭(Close)
close
长度和容量(Length and capacit)
Call Argument type Result
len(s) string type string length in bytes
[n]T, *[n]T array length (== n)
[]T slice length
map[K]T map length (number of defined keys)
chan T number of elements queued in channel buffer
cap(s) [n]T, *[n]T array length (== n)
[]T slice capacity
chan T channel buffer capacity
分配(Allocation)
new(T)
创建(Making slices, maps and channels)
Call Type T Result
make(T, n) slice slice of type T with length n and capacity n
make(T, n, m) slice slice of type T with length n and capacity m
make(T) map map of type T
make(T, n) map map of type T with initial space for n elements
make(T) channel unbuffered channel of type T
make(T, n) channel buffered channel of type T, buffer size n
例如：
s := make([]int, 10, 100) // slice with len(s) == 10, cap(s) == 100
s := make([]int, 1e3) // slice with len(s) == cap(s) == 1000
s := make([]int, 1<<63) // illegal: len(s) is not representable by a value of type int
s := make([]int, 10, 0) // illegal: len(s) > cap(s)
c := make(chan int, 10) // channel with a buffer size of 10
m := make(map[string]int, 100) // map with initial space for 100 elements
分片的追加(Appending to slices)
append(s S, x ...T) S // T is the element type of S
例如：
s0 := []int{0, 0}
s1 := append(s0, 2) // append a single element s1 == []int{0, 0, 2}
s2 := append(s1, 3, 5, 7) // append multiple elements s2 == []int{0, 0, 2, 3, 5, 7}
s3 := append(s2, s0...) // append a slice s3 == []int{0, 0, 2, 3, 5, 7, 0, 0}
s4 := append(s3[3:6], s3[2:]...) // append overlapping slice s4 == []int{3, 5, 7, 2, 3, 5, 7, 0, 0}
var t []interface{}
t = append(t, 42, 3.1415, "foo") // t == []interface{}{42, 3.1415, "foo"}
var b []byte
b = append(b, "bar"...) // append string contents b == []byte{'b', 'a', 'r' }
分片的复制(Copying slices)
copy(dst, src []T) int
copy(dst []byte, src string) int
例如：
var a = [...]int{0, 1, 2, 3, 4, 5, 6, 7}
var s = make([]int, 6)
var b = make([]byte, 5)
n1 := copy(s, a[0:]) // n1 == 6, s == []int{0, 1, 2, 3, 4, 5}
n2 := copy(s, s[2:]) // n2 == 4, s == []int{2, 3, 4, 5, 4, 5}
n3 := copy(b, "Hello, World!") // n3 == 5, b == []byte("Hello")
字典成员的删除(Deletion of map elements)
delete(m, k) // remove element m[k] from map m
复数的操作(Manipulating complex numbers)
complex(realPart, imaginaryPart floatT) complexT
real(complexT) floatT
imag(complexT) floatT
例如：
var a = complex(2, -2) // complex128
const b = complex(1.0, -1.4) // untyped complex constant 1 - 1.4i
x := float32(math.Cos(math.Pi/2)) // float32
var c64 = complex(5, -x) // complex64
var s uint = complex(1, 0) // untyped complex constant 1 + 0i can be converted to uint
_ = complex(1, 2<<s) // illegal: 2 assumes floating-point type, cannot shift
var rl = real(c64) // float32
var im = imag(a) // float64
const c = imag(b) // untyped constant -1.4
_ = imag(3 << s) // illegal: 3 assumes complex type, cannot shift
panic处理(Handling panics)
panic(interface{})
func recover() interface{}
例如：
func protect(g func()) {
defer func() {
log.Println("done") // Println executes normally even if there is a panic
if x := recover(); x != nil {
log.Printf("run time panic: %v", x)
}
}()
log.Println("start")
g()
}
自举函数(Bootstrapping)
Function Behavior
print prints all arguments; formatting of arguments is implementation-specific
println like print but prints spaces between arguments and a newline at the end