英文:
Is it possible to return a different number of values based on how many variables are assigned to the function?
问题
我有一个函数foo()，它返回一个int和一个bool，其中bool表示函数是否执行成功。如果调用者只想要int，他可以输入value, _ := foo()。有没有办法设置这样的方式，使得调用者只需输入value := foo()，它自动只返回int，就像range可以返回索引和值，或者只返回索引一样？
示例代码：
func foo(num int) (int, bool) {
if num % 2 == 1 {
//函数失败
return 0, false
}
//函数成功
return num + 5, true
}
func main() {
value1, _ := foo(6) //可以工作
value2 := foo(6) //赋值类型不匹配
}
英文:
I have a function, foo(), that returns an int and a bool, the bool being whether or not the function executed properly. If the caller only wants the int, he can type value, _ := foo(). Is there a way to set it so that the caller can just type value := foo() and it automatically only returns the int, like how range can return either the index and value, or just the index?
Example code:
func foo(num int) (int, bool) {
if num % 2 == 1 {
//function fails
return 0, false
}
//function succeeds
return num + 5, true
}
func main() {
value1, _ := foo(6) //works
value2 := foo(6) //assignment mismatch
}
答案1
得分: 2
Go编程语言的特殊功能包括映射（Maps）、类型断言（Type Assertions）、带有range子句的for语句以及通道接收具有可变数量的返回值。但对于常规函数类型，返回值的数量不能是可变的。
- 映射（Maps）
m := make(map[string]int)
m["one"] = 1
// 返回值是给定键的映射值。
val := m["one"]
// 第一个返回值是给定键的映射值，第二个返回值指示键是否存在于映射中。
val, ok := m["one"]
- 带有
range子句的for语句
arr := []int{1, 2, 3, 4}
// 返回值是索引。
for idx := range arr {
...
}
// 第一个返回值是索引，第二个返回值是该索引处元素的副本。
for idx, val := range arr {
...
}
- 类型断言（Type Assertions）
var i interface{}
i = 1
// 第一个返回值是底层值，第二个返回值是一个布尔值，报告断言是否成功。
num, ok := i.(int)
// 返回值是底层值。
num := i.(int)
- 通道接收（Channel Receives）
c := make(chan int, 2)
c <- 12
c <- 21
// 返回值表示从通道接收到的值。
val := <-c
// 第一个返回值是从通道接收到的值。第二个返回值是一个布尔值，指示是否没有更多的值可接收并且通道是否已关闭。
val, ok := <-c
英文:
Special features of the Go programming language include maps, type assertions, for statement with a range clause and channel receives have variable number of return values. But the number of return values cannot be variable for a regular function type.
- Maps
m := make(map[string]int)
m["one"] = 1
// Return value is the value in the map for the given key.
val := m["one"]
// First return value is the value in the map for the given
// key and second return value indicates if the key was
// present in the map.
val,ok := m["one"]
forstatement with arangeclause
arr := []int{1, 2, 3, 4}
// Return value is the index.
for idx := range arr {
...
}
// First return value is the index and second return
// value is a copy of the element at that index.
for idx, val := range arr {
...
}
- Type assertions
var i interface{}
i = 1
// First return value is the underlying value and second
// return value is a boolean value that reports whether the
// assertion succeeded or not.
num, ok := i.(int)
// Return value is the underlying value.
num := i.(int)
- Channels receives
c := make(chan int, 2)
c <- 12
c <- 21
// Return value indicates the received value from the channel.
val := <-c
// First return value is the received value from the
// channel. Second return value is a boolean which indicates
// if there are no more values to receive and the channel is
// closed or not.
val, ok := <-c
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