Why Can't I Range Over a Pointer to a Slice in Go?

Go's Inability to Range over Pointer to a Slice

In Go, it's common to encounter the error "cannot range over pointer to slice" when attempting to iterate over a slice pointer. This error stems from a mistaken assumption that the pointer would be automatically dereferenced during iteration.

Unfortunately, Go does not implicitly dereference pointer-to-slice types. The reason for this is that slices themselves act as pointers to arrays. Passing a slice to a function already gives the function access to the underlying data, eliminating the need for an additional pointer.

As explained in the book "Effective Go," "If a function takes a slice argument, changes it makes to the elements of the slice will be visible to the caller, analogous to passing a pointer to the underlying array."

Internally, a slice is composed of:

• A pointer to the first element in the underlying array
• The length of the slice
• The capacity of the slice

This compact structure makes the pointer unnecessary, leading to the inability to range over a pointer to a slice.

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