Go Variadic Function

Uses of Variadic Functions

At certain times we do not know how many string arguments will be needed for our functions. This is the point where variadic functions come into play. 

Variadic functions let us define functions that take an arbitrary number of arguments. This prevents us from coding against every possible variation of the input length.

This concept transfers across many different languages, such as Python and Java.

Example:

package main

import (
	"fmt"
)

func myVariadicFunction(args ...string) {
		fmt.Println(args)
}

func main() {
myVariadicFunction("hello", "world")
}

Command:

$ go run main.go

Output:  

[hello world]

 Note: If we try to run this, we should see our call to ‘fmt.Println()’ will print an array of strings which include ‘hello’ and ‘world’.

Variadic Functions are not limited to strings. We can also use any variation of composite or basic types.

In another example below, we will see how we are going to print s[0], the first and s[3], the fourth argument value that is passed to variadicExample() function.

Example:

package main

import "fmt"

func main() {
		variadicExample("red", "blue", "green", "yellow")
}
func variadicExample(s ...string) {
		fmt.Println(s[0])
		fmt.Println(s[3])
}

Output:

red
yellow
 

One requires being precise when running an empty function call. If the code inside of the function expects an argument and the absence of an argument will generate an error "panic: run-time error: index out of range". In the above example, you have to pass at least 4 arguments.

Multiple Arguments

The parameters accept an infinite number of arguments. The tree-dotted ellipsis tells the compiler that this string will accept from zero to multiple values.

Example:

package main
import "fmt"

func main() {
		variadicExample()
		variadicExample("red", "blue")
		variadicExample("red", "blue", "green")
		variadicExample("red", "blue", "green", "yellow")
}

func variadicExample(s ...string) {
		fmt.Println(s)
}

Output:

[]
[red blue]
[red blue green]
[red blue green yellow]

In the above example, the function has been called with single and multiple arguments; and without passing any arguments.
Uses of Variadic Function:

• The variadic functions are usually used for string formatting. 
• One can also pass multiple slices in the variadic function. 
• You can not use the variadic parameter as a return value, but you can return it as a slice.

Frequently Asked Questions

How is the declaration of the variadic function made?

In declaring the variadic function, the last parameter type is preceded by an ellipsis, i.e., (…). It shows that the function can be called at any number of parameters of this type.

How does “…type” behave inside the function?

Inside the function …type behaves and acts like a slice. For example, if we have a function signature, that, add( b…int)int, is now the parameter of type[]int.

Can an existing slice be passed in a variadic function?

One can also pass an existing slice in a variadic function. As expressed in the example, we pass a slice of the total array to the function.

What happens when one does not pass any argument in the variadic function?

When one does not pass any argument in the variadic function, then the slice inside the function is nil.

Can multiple slices be passed in the variadic function?

Yes, One can also pass multiple slices in the variadic function.

Can the Variadic parameter be used as a return value?

One can not use the variadic parameter as a return value, but you can return it as a slice.

When are the times when we use a Variadic function?

• Variadic function is used when one wants to pass a slice in a function.

• The variadic functions are commonly used for string formatting.

• Variadic function is used when one doesn't know the number of parameters.

How does using variadic function affect the readability of the program?

When you use the variadic function in your program, it increases the readability of your program.

Conclusion

In this blog, we have successfully covered the variadic functions in Golang. We also discussed what variadic functions are and how they can be used in your Go programs. We have also covered some examples for better understanding.

Refer to our courses and practice questions on Coding Ninjas Studio. You can also check out some other blogs on dynamics of Golang to follow.

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