github.com/benhoyt/goawk@v1.8.1/testdata/gawk/aryunasgn.awk (about)

     1  BEGIN {
     2      a[i] = "null"                         # i is initially undefined
     3      for (i in a) {                        # i is null string
     4          print length(i), a[i] # , typeof(i)  # 0 null
     5          print (i==0), (i=="")             # 1 1  should be  0 1
     6      }
     7      print a[""]                           # null
     8      print a[0]                            #
     9  
    10      b[$2] = "null also"                   # $2 is also undefined
    11      for (j in b) {
    12          print length(j), a[j] # , typeof(i)  # 0 null
    13          print (j==0), (j=="")             # 1 1  should be  0 1
    14      }
    15      print b[""]                           # null
    16      print b[0]                            #
    17  }