How to Avoid Memory Reallocation in Variadic Wrapper Functions?

Variadic Wrapper without Memory Reallocation

Variadic functions provide flexibility in parameter handling, but appending items to a wrapper function can trigger memory reallocation. This article explores solutions to avoid this issue while preserving debugging convenience.

One common approach to creating a variadic wrapper is to directly pass the arguments to the inner function:

<code class="go">func Debug(a ...interface{}) {
    if debug {
        fmt.Fprintln(out, prefix, sep, a...)
    }
}</code>

However, this can lead to "too many arguments" errors. Another approach is to use vararg to wrap the arguments, but this results in the error "name list not allowed in interface type."

A seemingly valid solution is to create a temporary slice and insert the prefix, separator, and arguments into it:

<code class="go">func Debug(a ...interface{}) {
    if debug {
        sl := make([]interface{}, len(a)+2)
        sl[0] = prefix
        sl[1] = sep
        for i, v := range a {
            sl[2+i] = v
        }

        fmt.Fprintln(out, sl...)
    }
}</code>

While this works, it involves unnecessary memory allocation.

Append as a Slick Solution

A more efficient approach is to utilize the append function. By appending the prefix and separator to the original arguments, we can avoid memory reallocation:

<code class="go">func Debug(a ...interface{}) {
    if debug {
        fmt.Fprintln(out, append([]interface{}{prefix, sep}, a...)...)
    }
}</code>

This one-liner effectively prepends the prefix and separator to the variadic arguments without creating a new slice. It is concise, efficient, and solves the memory allocation issue without compromising the functionality of the variadic wrapper.

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