Multiple distinct objects: Difference between revisions

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 =={{header|Nim}}==
+In Nim, copy semantic is the rule. So it is very easy to create multiple distinct objects.
-The simplest form of initialization works, but is a bit cumbersome to write:
-<lang nim>proc foo(): string =
-  echo "Foo()"
-  "mystring"
+We give some examples with sequences of sequences and sequences of references:
-let n = 100
-var ws = newSeq[string](n)
-for i in 0 .. <n: ws[i] = foo()</lang>
-If actual values instead of references are stored in the sequence, then objects can be initialized like this. Objects are distinct, but the initializer <code>foo()</code> is called only once, then copies of the resulting object are made:
-<lang nim>proc newSeqWith[T](len: int, init: T): seq[T] =
-  result = newSeq[T] len
-  for i in 0 .. <len:
-    result[i] = init
+<lang Nim>import sequtils, strutils
-var xs = newSeqWith(n, foo())</lang>
-To get the initial behaviour, where <code>foo()</code> is called to create each object, a template can be used:
-<lang nim>template newSeqWith2(len: int, init: expr): expr =
-  var result {.gensym.} = newSeq[type(init)](len)
-  for i in 0 .. <len:
-    result[i] = init
-  result
+# Creating a sequence containing sequences of integers.
-var ys = newSeqWith2(n, foo())</lang>
+var s1 = newSeq[seq[int]](5)
+for item in s1.mitems: item = @[1]
+echo "s1 = ", s1   # @[@[1], @[1], @[1], @[1], @[1]]
+s1[0].add 2
+echo "s1 = ", s1   # @[@[1, 2], @[1], @[1], @[1], @[1]]
+# Using newSeqWith.
+var s2 = newSeqWith(5, @[1])
+echo "s2 = ", s2   # @[@[1], @[1], @[1], @[1], @[1]]
+s2[0].add 2
+echo "s2 = ", s2   # @[@[1, 2], @[1], @[1], @[1], @[1]]
+# Creating a sequence containing pointers.
+proc newInt(n: int): ref int =
+  new(result)
+  result[] = n
+var s3 = newSeqWith(5, newInt(1))
+echo "s3 contains references to ", s3.mapIt(it[]).join(", ")   # 1, 1, 1, 1, 1
+s3[0][] = 2
+echo "s3 contains references to ", s3.mapIt(it[]).join(", ")   # 2, 1, 1, 1, 1
+# How to create non distinct elements.
+let p = newInt(1)
+var s4 = newSeqWith(5, p)
+echo "s4 contains references to ", s4.mapIt(it[]).join(", ")   # 1, 1, 1, 1, 1
+s4[0][] = 2
+echo "s4 contains references to ", s4.mapIt(it[]).join(", ")   # 2, 2, 2, 2, 2</lang>
 =={{header|OCaml}}==