What Is a Higher-Order Function in Go

A higher-order function in Go is a function that takes one or more functions as arguments or returns a function as its result. Because Go treats functions as first-class values, you can pass them around just like integers or strings. Here is a simple example using the archive/zip package to register a custom compressor, which is a function passed to another function:

w.RegisterCompressor(zip.Deflate, func(out io.Writer) (io.WriteCloser, error) {
    return flate.NewWriter(out, flate.BestCompression)
})

In this code, RegisterCompressor is the higher-order function because it accepts a function literal (the anonymous function) as its second argument to define custom behavior.

A higher-order function is simply a function that works with other functions. It can either take a function as an input to decide how to behave, or it can give you a new function back as a result. Think of it like a vending machine that doesn't just give you a snack, but instead lets you program exactly what snack it should dispense based on your specific rules.