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# setref(+Name, ?Value)

Sets the value of the named reference to Value.

Name
  Atom (name of a reference).
Value
  Prolog term.

## Description

If Name is the name of a (previously declared) reference, it will will be set to refer to the term Value.

A named reference can be used to hold a reference to a term, in the same way as a logical variable. Unlike a logical variable, the reference has a name under which it can be looked up. Its value is not a copy, but a reference to the actual Value. This implies that the value behaves logically, i.e. it disappears on backtracking, bindings to the variables inside it are undone on backtracking etc.

Changing the value of a reference is similar to changing an argument of a compound term using setarg/3. The change is undone on backtracking, i.e. the value of the reference reverts to what it was before being changed. A reference that has never been set (or whose settings were all undone by backtracking) has its declared initialization value.

Reference names are visible in the module where they are declared. Furthermore every ECLiPSe engine has its own reference store, meaning that the values are engine/thread-local and cannot be shared.

### Modes and Determinism

- setref(+, ?) is det

### Modules

This predicate is sensitive to its module context (tool predicate, see @/2).

### Exceptions

(4) instantiation fault
  Name is uninstantiated
(5) type error
  Name is not an atom.
(45) named object does not exist
  Name has not been declared as a reference.

## Examples

        ?- local reference(r, hello).
        Yes (0.00s cpu)

        ?- getref(r,X), setref(r,world), getref(r,Y).
        X = hello
        Y = world
        Yes (0.00s cpu)

        ?- getref(r,X), ( setref(r,world), fail ; getref(r,Y) ).
        X = hello
        Y = hello
        Yes (0.00s cpu)

## See Also

reference / 2, getref / 2, setarg / 3, swapref / 3