Deepcopy
Demonstrate how your language handles complete copying, often referred to as deepcopying, of complex data structures.
This can be via a built-in procedure or operator, a function from a common library (provide reference and source if it is written in the language), or a procedure (show source). Describe the relevant semantics of structures, such as if they are homogeneous or heterogeneous, or if they can contain loops. Describe any limitations of the method.
Demonstrate the procedure by copying a structure with all supported semantics/complexity (e.g. heterogeneous with loops).
Demonstrate that the structure and it's copy are different.
Icon and Unicon
Unicon and Icon support heterogeneous structures with loops. The Unicon book has an example of a simple algorithm for producing a deep copy of a structured value (set, list, table, or record); however, that code did not handle graph structures that are not trees. The code for deepcopy below from Unilib is a modification that addresses loops.
The code requires modification to run under Icon as Unicon extended key(X) to operate on lists and records not just tables.
<lang Unicon>procedure deepcopy(A, cache) #: return a deepcopy of A
local k
/cache := table() # used to handle multireferenced objects if \cache[A] then return cache[A]
case type(A) of {
"table"|"list": {
cache[A] := copy(A)
every cache[A][k := key(A)] := deepcopy(A[k], cache)
}
"set": {
cache[A] := set()
every insert(cache[A], deepcopy(!A, cache))
}
default: { # records and objects (encoded as records)
cache[A] := copy(A)
if match("record ",image(A)) then {
every cache[A][k := key(A)] := deepcopy(A[k], cache)
}
}
}
return .cache[A]
end</lang>
The following code demonstrates deepcopy usage and that the resulting structure is different from the original by comparing assignment, copy, and deepcopy.
<lang Icon>link printf,ximage
procedure main()
knot := makeknot() # create a structure with loops knota := knot # copy by assignment (reference) knotc := copy(knot) # built-in copy (shallow) knotdc := deepcopy(knot) # deep copy
showdeep("knota (assignment) vs. knot",knota,knot)
showdeep("knotc (copy) vs. knot",knotc,knot)
showdeep("knotdc (deepcopy) vs. knot",knotdc,knot)
xdump("knot (original)",knot)
xdump("knota (assignment)",knota)
xdump("knotc (copy)",knotc)
xdump("knotdc (deepcopy)",knotdc)
end
record rec1(a,b,c) # record for example
class Class1(a1,a2) # class - looks like a record under the covers
method one()
self.a1 := 1
return
end
initially
self.a1 := 0
end
procedure makeknot() #: return a homogeneous structure with loops
L := [9,8,7] T := table() T["a"] := 1 R := rec1(T) S := set(R) C := Class1() C.one() T["knot"] := [L,R,S,C] put(L,R,S,T,C) return L
end
procedure showdeep(tag,XC,X) #: demo to show (non-)equivalence of list elements
printf("Analysis of copy depth for %s:\n",tag)
showequiv(XC,X)
every showequiv(XC[i := 1 to *X],X[i])
end
procedure showequiv(x,y) #: show (non-)equivalence of two values
return printf(" %i %s %i\n",x,if x === y then "===" else "~===",y)
end</lang>
printf.icn provides printf ximage.icn provides xdump
The sample of output below compares all elements of a copy of a structure against the original. Immutable types like numbers, strings, and csets will show as the same (i.e. ===) and different mutable types will show as not the same (i.e. ~===). This clearly shows the difference between assignment, copy, and deepcopy.
Analysis of copy depth for knota (assignment) vs. knot: list_11(7) === list_11(7) 9 === 9 8 === 8 7 === 7 record rec1_2(3) === record rec1_2(3) set_2(1) === set_2(1) table_2(2) === table_2(2) record Class1__state_2(4) === record Class1__state_2(4) Analysis of copy depth for knotc (copy) vs. knot: list_13(7) ~=== list_11(7) 9 === 9 8 === 8 7 === 7 record rec1_2(3) === record rec1_2(3) set_2(1) === set_2(1) table_2(2) === table_2(2) record Class1__state_2(4) === record Class1__state_2(4) Analysis of copy depth for knotdc (deepcopy) vs. knot: list_14(7) ~=== list_11(7) 9 === 9 8 === 8 7 === 7 record rec1_3(3) ~=== record rec1_2(3) set_3(1) ~=== set_2(1) table_4(2) ~=== table_2(2) record Class1__state_3(4) ~=== record Class1__state_2(4) ...
Another way to show the difference in the structures is to use the xdump procedure will produce the following in stderr (&errout):
knot (original)"
L11 := list(7)
L11[1] := 9
L11[2] := 8
L11[3] := 7
L11[4] := R_rec1_2 := rec1()
R_rec1_2.a := T2 := table(&null)
T2["a"] := 1
T2["knot"] := L12 := list(4)
L12[1] := L11
L12[2] := R_rec1_2
L12[3] := S2 := set()
insert(S2,R_rec1_2)
L12[4] := R_Class1__state_2 := Class1__state()
R_Class1__state_2.a1 := 1
L11[5] := S2
L11[6] := T2
L11[7] := R_Class1__state_2
...