How to Pass a Slice of Slices as Variadic Arguments in Go?

Passing Unpacked Slices as Variadic Arguments

In Go, variadic functions accept an indefinite number of arguments of a specific type. When passing a slice of slices to such a function, it is crucial to understand the type conversion and unpacking mechanisms involved.

If the slice contains elements of the same type as the variadic parameter, the slice can be passed without unpacking. However, if the slice contains a mixture of types or slices within slices, the situation becomes more complex.

According to the Go specification, if the final argument to a variadic function is assignable to a slice type, it can be passed unchanged as the value for the variadic parameter if it is followed by .... This means that no new slice will be created.

In the case of a slice of slices, the slice itself cannot be assigned to the variadic parameter (of type []interface{}). This is why an error is thrown when attempting to pass sliceOfSlices... to the unpack function.

To resolve this issue, an intermediary step is required. A new slice of the appropriate type ([]interface{} in this case) must be created and the elements of the slice of slices copied into it. This new slice can then be passed to the unpack function using ....

For example:

<code class="go">var sliceOfSlices2 []interface{}
for _, v := range sliceOfSlices {
    sliceOfSlices2 = append(sliceOfSlices2, v)
}

unpack(sliceOfSlices2...)</code>

This approach ensures that each element of the slice of slices is passed separately to the unpack function, as intended.

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