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  lt host gt  www google de  lt port gt  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   lt host gt            arguments   lt port gt      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

User · Accepted Answer

You need to add type assertion   string   It is necessary because the map is of type map string interface     host    arguments   lt host gt     string          arguments   lt port gt     string    Latest version of Docopt returns Opts object that has methods for conversion   host  err    arguments String   lt host gt    port  err    arguments String   lt port gt    host port    host         port

User · Answer

You don t need to use a type assertion  instead just use the  v format specifier with Sprintf   hostAndPort    fmt Sprintf   v  v   arguments   lt host gt     arguments   lt port gt

User · Answer

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

[go] How to convert interface{} to string?

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