Added module pointers containing toUncheckedArray

Author: timotheecour

changelog.md

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+## additions and changes
+
+- Added module `pointers` containing `toUncheckedArray`

src/fusion/pointers.nim

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+##[
+Convenience procs to deal with pointer-like variables.
+]##
+
+proc toUncheckedArray*[T](a: ptr T): ptr UncheckedArray[T] {.inline.} =
+  ## Shortcut for `cast[ptr UncheckedArray[T]](a)`, where T is inferred.
+  ## This allows array indexing operations on `a`.
+  ## This is unsafe as it returns `UncheckedArray`.
+  runnableExamples:
+    var a = @[10, 11, 12]
+    let pa = a[1].addr.toUncheckedArray
+    doAssert pa[-1] == 10
+    pa[0] = 100
+    doAssert a == @[10, 100, 12]
+    pa[0] += 5
+    doAssert a[1] == 105
+  cast[ptr UncheckedArray[T]](a)