如何将interface {}转换为字符串？

Question

I'm using docopt to parse command-line arguments. This works, and it results in a map, such as

map[<host>:www.google.de <port>:80 --help:false --version:false]

Now I would like to concatenate the host and the port value to a string with a colon in-between the two values. Basically, something such as:

host := arguments["<host>"] + ":" + arguments["<port>"]

Unfortunately, this doesn't work, as I get the error message:

invalid operation: arguments[""] + ":" (mismatched types interface {} and string)

So obviously I need to convert the value that I get from the map (which is just interface{} , so it can be anything) to a string. Now my question is, how do I do that?

Answer 1

You need to add type assertion .(string) . It is necessary because the map is of type map[string]interface{} :

host := arguments["<host>"].(string) + ":" + arguments["<port>"].(string)

Latest version of Docopt returns Opts object that has methods for conversion:

host, err := arguments.String("<host>")
port, err := arguments.String("<port>")
host_port := host + ":" + port

Answer 2

您不需要使用类型断言，而只需在Sprintf使用%v格式说明符：

hostAndPort := fmt.Sprintf("%v:%v", arguments["<host>"], arguments["<port>"])

Answer 3

To expand on what Peter said: Since you are looking to go from interface{} to string, type assertion will lead to headaches since you need to account for multiple incoming types. You'll have to assert each type possible and verify it is that type before using it.

Using fmt.Sprintf ( https://golang.org/pkg/fmt/#Sprintf ) automatically handles the interface conversion. Since you know your desired output type is always a string, Sprintf will handle whatever type is behind the interface without a bunch of extra code on your behalf.

Answer 4

Now i was created package for converting interface to any data type here the github link and godoc link https://github.com/mufti1/interconv

godoc link https://godoc.org/github.com/mufti1/interconv/package

you just import from godoc and then call the function