英文:
Is there autovivification for Go?
问题
在Go语言中是否有自动创建嵌套结构的功能（autovivification）？
正如@JimB正确指出的那样，我的定义并不那么严格。关于我的目标：在Python中，我们有一种非常优雅的“模拟”自动创建嵌套结构的方法：
type Path map[string]interface{}
func (p Path) Get(key string) interface{} {
if val, ok := p[key]; ok {
return val
}
p[key] = make(Path)
return p[key]
}
在Go语言中是否有类似的解决方案？
英文:
Is there autovivification for Go?
As @JimB correctly noticed, my definition is not that strict. About my goal: In Python we have a very elegant "emulation" for an autovivification:
class Path(dict):
def __missing__(self, key):
value = self[key] = type(self)()
return value
Is there a similar solution for Go?
答案1
得分: 4
如果键不存在或地图为nil，Go的映射将返回该类型的零值。
https://play.golang.org/p/sBEiXGfC1c
var sliceMap map[string][]string
// slice是一个nil []string
slice := sliceMap["不存在的键"]
var stringMap map[string]string
// s是一个空字符串
s := stringMap["不存在的键"]
由于具有数值值的映射在缺少条目时返回0，Go允许您在不存在的键上使用递增和递减运算符：
counters := map[string]int{}
counters["one"]++
英文:
Go maps will return a zero value for the type if the key doesn't exist, or the map is nil
https://play.golang.org/p/sBEiXGfC1c
var sliceMap map[string][]string
// slice is a nil []string
slice := sliceMap["does not exist"]
var stringMap map[string]string
// s is an empty string
s := stringMap["does not exist"]
Since a map with numeric values return will return 0 for missing entries, Go lets you use the increment and decrement operators on non-existent keys:
counters := map[string]int{}
counters["one"]++
答案2
得分: 1
此外，扩展JimB的答案，通过使用map、interface{}和type assertion的组合，您可以动态创建任何复杂的结构：
type Obj map[interface{}]interface{}
func main() {
var o Obj
o = Obj{
"Name": "Bob",
"Age": 23,
3: 3.14,
}
fmt.Printf("%+v\n", o)
o["Address"] = Obj{"Country": "USA", "State": "Ohio"}
fmt.Printf("%+v\n", o)
o["Address"].(Obj)["City"] = "Columbus"
fmt.Printf("%+v\n", o)
fmt.Printf("City = %v\n", o["Address"].(Obj)["City"])
}
输出结果（在Go Playground上尝试）：
map[Name:Bob Age:23 3:3.14]
map[Age:23 3:3.14 Address:map[Country:USA State:Ohio] Name:Bob]
map[3:3.14 Address:map[Country:USA State:Ohio City:Columbus] Name:Bob Age:23]
City = Columbus
[1]: https://golang.org/ref/spec#Type_assertions
[2]: https://play.golang.org/p/Q30UxRJ5H1
英文:
Also extending JimB's answer, with the combination of map, interface{} and type assertion, you can dynamically create any complex structures:
type Obj map[interface{}]interface{}
func main() {
var o Obj
o = Obj{
"Name": "Bob",
"Age": 23,
3: 3.14,
}
fmt.Printf("%+v\n", o)
o["Address"] = Obj{"Country": "USA", "State": "Ohio"}
fmt.Printf("%+v\n", o)
o["Address"].(Obj)["City"] = "Columbus"
fmt.Printf("%+v\n", o)
fmt.Printf("City = %v\n", o["Address"].(Obj)["City"])
}
Output (try it on the Go Playground):
map[Name:Bob Age:23 3:3.14]
map[Age:23 3:3.14 Address:map[Country:USA State:Ohio] Name:Bob]
map[3:3.14 Address:map[Country:USA State:Ohio City:Columbus] Name:Bob Age:23]
City = Columbus
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