New vs named return as pointer in go

My function is working file with this signature

func GetFileMetadata(f *multipart.FileHeader) *FileMetadata {
    d := new(FileMetadata)

    // ...

    if typ, err := GetFileRealType(f); err == nil {
        d.Type = typ.MIME.Value
        fileExt = "." + typ.Extension
    } else {
        d.Type = "unknown"
    }

    return d
}

With following signature it doesn’t.

func GetFileMetadata(f *multipart.FileHeader) (d *FileMetadata) {

    // ...

    if typ, err := GetFileRealType(f); err == nil {
        d.Type = typ.MIME.Value
        fileExt = "." + typ.Extension
    } else {
        d.Type = "unknown"
    }

    return
}

Getting nil pointer dereference err. What is the reason?

>Solution :

When you use a named return variable, that variable is declared within the function body with an initial value set to its zero value. So in your second example where you used a named return with d, d is a nil pointer. You should still initialize it:

    d = new(FileMetadata)