What are variadic functions in Go, and how do I define them?
Jun 21, 2025 pm 02:13 PMThe variable parameter functions in Go are defined before the parameter type, such as func sum(nums...int), allowing any number of parameters to be passed, and are processed internally in slice. 1. When defining, you need to place the variable parameters at the end and there can only be one; 2. When calling, you can use multiple values ??or slice parameters with...; 3. It is suitable for logs, summary and other scenarios, but it is not suitable for a large number of parameters or the meaning of each parameter is clear. Pay attention to the small performance overhead caused by changing parameters to slices when using them.
Variadic functions in Go are functions that can accept a variable number of arguments. This feature is handy when you want to write flexible functions that can handle different numbers of inputs without overloading or using slices explicitly.
You've probably seen them used in standard packages like fmt.Println
, which can take one, two, or more arguments and still work the same way.
How to Define a Variadic Function
In Go, you define a variadic function by placing an ellipsis ( ...
) before the type of the last parameter in the function signature. That tells Go that this function can be called with any number of arguments for that parameter.
For example:
func sum(nums ...int) int { total := 0 for _, num := range nums { total = num } Return total }
Now you can call it like this:
sum(1, 2) sum(1, 2, 3, 4, 5)
The function will receive all those values ??as a slice, so inside the function body, you can loop through them or process them however you need.
A few things to note:
- The variadic parameter must be the last one in the list.
- You can only have one variadic parameter per function.
Passing a Slice to a Variadic Function
If you already have a slice and want to pass its elements as individual arguments to a variadic function, just add ...
after the slice when calling the function.
Example:
values ??:= []int{1, 2, 3, 4} result := sum(values...) // Pass each element as separate argument
This makes it easy to combine slices and variadic functions without manually unpacking everything.
But don't try to do this with arrays unless you convert them first — the ...
syntax works with slices, not arrays directly.
When to Use Variadic Functions
Use variadic functions when your logic benefits from having optional or multiple inputs in a clean way. They're especially useful for:
- Logging or printing functions (like
fmt.Printf
) - Helper utilities that collect values ??(like concatenation, summation)
- Configurable options where defaults are used unless overridden
They're less ideal if:
- You expect a large number of arguments (can get messy)
- Each argument has distinct meaning and needs a name (better to use a struct)
Also, remember that variadic parameters become slices inside the function, so if you're doing performance-sensitive code, keep in mind the small overhead of creating that slice on each call.
So that's how variadic functions work in Go. Basically, just use ...T
in the function definition and treat the input like a slice inside the function. Not too bad once you get the hang of it.
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