How Can You Achieve Generic Programming with Variadic Functions in Go?

Generic Programming with Variadic Functions in Go

Despite Go's lack of templates or function overloading, achieving some degree of generic programming for variadic functions is possible.

Consider the following redundant code snippets:

<code class="go">func (this Document) GetString(name string, defaults ...string) string {
    v, ok := this.GetValueFromDb(name)
    if !ok {
        if len(defaults) >= 1 {
            return defaults[0]
        } else {
            return ""
        }
    }
    return v.asString
}

func (this Document) GetInt(name string, defaults ...int) int {
    v, ok := this.GetValueFromDb(name)
    if !ok {
        if len(defaults) >= 1 {
            return defaults[0]
        } else {
            return 0
        }
    }
    return v.asInt
}</code>

To eliminate this redundancy, we can utilize the interface{} type:

<code class="go">func (this Document) Get(name string, defaults ...interface{}) interface{} {
    v, ok := this.GetValueFromDb(name)
    if !ok {
        if len(defaults) >= 1 {
            return defaults[0]
        } else {
            return nil
        }
    }
    return v
}</code>

This general function can then be used with type assertion in client code:

<code class="go">value := document.Get("index", 1).(int)  // Panics if the value is not an int</code>

or

<code class="go">value, ok := document.Get("index", 1).(int)  // `ok` is false if the value is not an int</code>

However, this approach introduces runtime overhead. It may be more efficient in some cases to retain the separate functions and consider restructuring the code.

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