How to convert interface{} to string?

go
Golo Roden picture Golo Roden · Nov 25, 2014 · Viewed 143.5k times · Source

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

Grzegorz Żur picture Grzegorz Żur · Nov 25, 2014

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

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