How Can I Set Default Values for Function Parameters in Go?

Setting Default Values in Go Functions

While Go does not provide a native way to specify default values in function parameters, several alternative approaches can achieve this functionality.

Option 1: Caller-Controlled Defaults

In this approach, the caller can explicitly specify default values by checking if a parameter is empty or zero. For example:

func SaySomething(i string) string {
  if i == "" {
    i = "Hello"
  }

  return i
}

Option 2: Optional Parameters

You can define a parameter as optional by placing it at the end of the parameter list. In this case, the function will use a default value if no argument is provided.

func Concat(a string, b int) string {
  if b == 0 {
    b = 5
  }

  return a + strconv.Itoa(b)
}

Option 3: Configuration Struct

Create a struct with default values for your function's parameters. This provides a declarative way to set defaults.

type Config struct {
  Name string `default:"John Doe"`
  Age  int    `default:"0"`
}

func Greet(c Config) string {
  return fmt.Sprintf("Hello, %s! You are %d years old.", c.Name, c.Age)
}

Option 4: Variadic Arguments

This approach allows you to parse incoming arguments and set default values accordingly.

func ProcessArgs(args ...interface{}) {
  a := "default-a"
  b := 5

  for _, arg := range args {
    switch v := arg.(type) {
      case string:
        a = v
      case int:
        b = v
    }
  }

  // Use a and b
}

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