Why Does Go Throw a 'cannot range over pointer to slice' Error?

Go: Iterating over Pointers to Slices

When working with Go slices, it's important to understand how pointers and slices interact. The provided code throws a "cannot range over pointer to slice" error because it attempts to iterate over a pointer to a slice without dereferencing it.

A slice is a flexible data structure that points to an array. While it shares some similarities with pointers, it differs in that a slice already encapsulates a pointer to the underlying array. Thus, creating a pointer to a slice serves no purpose and can lead to confusion.

In the code snippet, the error occurs in the populateClassRelationships function, specifically in the line:

for i := range classes {

classes := new([]entities.Class)

Instead of using a pointer to a slice (*[]entities.Class), the correct approach is to pass the slice itself, as seen in the modified code:

func (c *ClassRepository) ClassesForLastNDays(days int) []entities.Class {
    classes := new([]entities.Class)

By modifying the code in this way, Go automatically dereferences the slice and allows for proper iteration. Refer to the official Go documentation for more information on slices and pointers.

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