How to convert interface{} to string?

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?

Gopher · Accepted Answer

you want a type assertion: // will panic if host is not type int host := arguments[""].(string) // Alt. non panicking version host, ok := arguments[""].(string) You need to add type assertion .(string). It is necessary because the map is of type map[string]interface{}: host := arguments[""].(string) + ":" + arguments[""].(string) Latest version of Docopt returns Opts object that has methods for conversion: host, err := arguments.String("") port, err := arguments.String("") host_port := host + ":" + port

Go Language

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