How to Convert a Slice of Structs to a Slice of Interfaces in Go?

Converting Slice of Structs to Slice of Interface

When attempting to assign a slice of structs to a slice of interfaces, such as in the case of passing data to AppEngine's datastore.PutMulti, you may encounter compilation errors due to type incompatibility. The error likely reads, "cannot use type []*MyStruct as type []interface { } in assignment."

To understand this issue, it's essential to recognize that assigning a slice of structs to a slice of interfaces involves more than a simple type conversion. Instead, each struct element must be individually wrapped within an interface. This process creates a pointer to the original struct and includes a descriptor for its type.

As a result, there is no direct or automated way to copy a slice of structs into a slice of interfaces. Each element must be explicitly copied and wrapped within an interface to achieve the desired output. Therefore, the only viable solution is to perform the assignment one element at a time.

Consider the following snippet as an example:

var src []*MyStruct = append(src, &MyStruct {...})
var dest []interface{}
for _, s := range src {
    dest = append(dest, s)
}

In this example, the slice of structs is iterated over, and each struct is appended to the slice of interfaces by wrapping it in an interface explicitly. While this process may be tedious, it is the only method to successfully convert a slice of structs to a slice of interfaces.

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