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707 :: addr() equivalent for ref?

• mapdog (orginal) [2015-01-01T22:14:34+01:00] view original

  You can make a pointer with addr, but not a ref.

  let x: ptr T = addr(y)
  # vs
  let x: ref T = newRef(y)
  Run

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• skyfex (orginal) [2015-01-02T01:30:26+01:00] view original

  You can't get a ref of a variable, because it's unsafe, and ref's are supposed to be safe to use.

  Let's say you allocate an object on the stack (when you type let y: SomeThing), then hypothetically get a reference of it (let x = getRef(y)), then pass it to a procedure, that procedure is now allowed to store that reference in a global variable or another object. Later your variable y goes out of scope, but you can still have references to it, which are now invalid.

  You can of course copy the content of y into a new allocated ref. E.g.

  
  var x: ref T
  new(x)
  x[] = y
  Run

  If you want to be able to do this in one procedure it should be possible to write one.

  See: http://nim-lang.org/tut1.html#reference-and-pointer-types

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• mapdog (orginal) [2015-01-03T14:38:09+01:00] view original

  I was thinking about strings and seq, and being able to reference one without copying it. Its not known what a string or seq is. Is it a reference to a heap object? If so, you should be able to make a new reference to it.

  str = "abc"
  refStr: ref string
  # refStr = ref(str) not possible
  Run

  I just discovered you can

  str1: ref String = new(string)
  str1[] = "abc"
  str2: ref string = str1
  Run

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• Varriount (orginal) [2015-01-04T00:09:26+01:00] view original

  mapdog: If you want to copy the reference of a string/sequence, rather than the contents, use the shallowAssign procedure. String and sequences are always references to heap objects (unless, in the future, nim starts using alloca for certain things)

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