new tasks

Task/Deepcopy/0DESCRIPTION

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+Demonstrate how to copy data structures containing complex hetrogeneous and cyclic semantics. This is often referred to as [[wp:Deep_copy#Deep_copy|deep copying]], and is normally required where structures are mutable and to ensure that independent copies can be manipulated without side-effects.
+
+If this facility is not built into the language, it is permissible to use functions from a common library, or a coded procedure.
+
+The task should show:
+
+* Relevant semantics of structures, such as their [[wp:Homogeneity and heterogeneity|homogeneous or heterogeneous]] properties, or containment of (self- or mutual-reference) cycles.
+
+* Any limitations of the method.
+
+* That the structure and its copy are different.
+
+* Suitable links to external documentation for common libraries.

Task/Deepcopy/Go/deepcopy-2.go

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+package main
+
+import (
+    "encoding/gob"
+    "fmt"
+    "os"
+)
+
+// capability requested by task
+func deepcopy(dst, src interface{}) error {
+    r, w, err := os.Pipe()
+    if err != nil {
+        return err
+    }
+    enc := gob.NewEncoder(w)
+    err = enc.Encode(src)
+    if err != nil {
+        return err
+    }
+    dec := gob.NewDecoder(r)
+    return dec.Decode(dst)
+}
+
+// define linked list type, an example of a recursive type
+type link struct {
+    Value string
+    Next  *link
+}
+
+// method satisfies stringer interface for fmt.Println
+func (l *link) String() string {
+    if l == nil {
+        return "nil"
+    }
+    s := "(" + l.Value
+    for l = l.Next; l != nil; l = l.Next {
+        s += " " + l.Value
+    }
+    return s + ")"
+}
+
+func main() {
+    // create a linked list with two elements
+    l1 := &link{"a", &link{Value: "b"}}
+    // print original
+    fmt.Println(l1)
+    // declare a variable to hold deep copy
+    var l2 *link
+    // copy
+    if err := deepcopy(&l2, l1); err != nil {
+        fmt.Println(err)
+        return
+    }
+    // print copy
+    fmt.Println(l2)
+    // now change contents of original list
+    l1.Value, l1.Next.Value = "c", "d"
+    // show that it is changed
+    fmt.Println(l1)
+    // show that copy is unaffected
+    fmt.Println(l2)
+}

Task/Deepcopy/Go/deepcopy.go

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+package main
+
+import "fmt"
+
+// a complex data structure
+type cds struct {
+    i int            // no special handling needed for deep copy
+    s string         // no special handling
+    b []byte         // copied easily with append function
+    m map[int]bool   // deep copy requires looping
+}
+
+// a method
+func (c cds) deepcopy() *cds {
+    // copy what you can in one line
+    r := &cds{c.i, c.s, append([]byte{}, c.b...), make(map[int]bool)}
+    // populate map with a loop
+    for k, v := range c.m {
+        r.m[k] = v
+    }
+    return r
+}
+
+// demo
+func main() {
+    // create and populate a structure
+    c1 := &cds{1, "one", []byte("unit"), map[int]bool{1: true}}
+    fmt.Println(c1)      // show it
+    c2 := c1.deepcopy()  // copy it
+    fmt.Println(c2)      // show copy
+    c1.i = 0             // change original
+    c1.s = "nil"
+    copy(c1.b, "zero")
+    c1.m[1] = false
+    fmt.Println(c1)      // show changes
+    fmt.Println(c2)      // show copy unaffected
+}

Task/Deepcopy/JavaScript/deepcopy-2.js

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+var deepcopy = function(o){
+  return eval(uneval(o));
+};
+var src = {foo:0,bar:[0,1]};
+src['baz'] = src;
+print(uneval(src));
+var dst = deepcopy(src);
+print(uneval(src));

Task/Deepcopy/JavaScript/deepcopy.js

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+var deepcopy = function(o){
+  return JSON.parse(JSON.stringify(src));
+};
+
+var src = {foo:0,bar:[0,1]};
+print(JSON.stringify(src));
+var dst = deepcopy(src);
+print(JSON.stringify(src));