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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?
951
interface{} means you can put value of any type, including your own custom type. All types in Go satisfy an empty interface ( interface{} is an empty interface). In your example, Msg field can have value of any type.
Implementing an interface in Go To implement an interface, you just need to implement all the methods declared in the interface. Unlike other languages like Java, you don't need to explicitly specify that a type implements an interface using something like an implements keyword.
Type assertions in Golang provide access to the exact type of variable of an interface. If already the data type is present in the interface, then it will retrieve the actual data type value held by the interface. A type assertion takes an interface value and extracts from it a value of the specified explicit type.
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 You don't need to use a type assertion, instead just use the %v format specifier with Sprintf:
hostAndPort := fmt.Sprintf("%v:%v", arguments["<host>"], arguments["<port>"]) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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