Simulating Named and Optional Parameters

Before getting to Go’s unique function features, I’ll mention two that Go doesn’t have: named and optional input parameters. With one exception, which I will cover in the next section, you must supply all the parameters for a function. If you want to emulate named and optional parameters, define a struct that has fields that match the desired parameters and pass the struct to your function. Example 4-1 demonstrates this pattern.

Example 4-1. Using a struct to simulate named parameters

type MyFuncOpts struct {
    FirstName string
    LastName  string
    Age       int
}

func MyFunc(opts MyFuncOpts) error {
    // do something here
}

func main() {
    MyFunc(MyFuncOpts{
        LastName: "Patel",
        Age:      50,
    })
    MyFunc(MyFuncOpts{
        FirstName: "Joe",
        LastName:  "Smith",
    })
}

The code for this program is in the examples/named_optional_parameters directory.

In practice, not having named and optional parameters isn’t a limitation. A function shouldn’t have more than a few parameters, and named and optional parameters are mostly useful when a function has many inputs. If you find yourself in that situation, your function is quite possibly too complicated.