How does one get a `var` from a `ref` object?

[adnan]

I think the code and the error message explains it better:
    
    
    import options, sequtils
    
    type
        Person = object
            id: int
            name: string
        Spouse = object
            base: ref Person
            engagedTo: Option[ref Person]
            preferences: seq[ref Person]
        Population = object
            males, females: seq[ref Spouse]
    
    proc newPerson(name: string; isMale: bool): Person =
        if isMale:
            var nextMaleId {.global.} = 1
            result.id = nextMaleId
            inc nextMaleId
        else:
            var nextFemaleId {.global.} = -1
            result.id = nextFemaleId
            dec nextFemaleId
        result.name = name
    
    proc newSpouse(base: ref Person; preferences: openArray[ref Person]): 
Spouse =
        result.base = base
        result.preferences = preferences.toSeq()
    
    proc isSingle(spouse: ref Spouse): bool = spouse.engagedTo.isNone()
    
    proc prefersMoreThanCurrent(baseSpouse: ref Spouse;
            probePerson: ref Person): Option[bool] =
        if baseSpouse.isSingle():
            result = some(true)
        else:
            for refPerson in baseSpouse.preferences:
                if refPerson.id == probePerson.id:
                    result = some(true)
                    break
                if refPerson.id == baseSpouse.engagedTo.unsafeGet().id:
                    result = some(false)
                    break
    
    proc newPopulation(males, females: openArray[ref Spouse]): 
Option[Population] =
        let dim = males.len()
        if males.len() == females.len():
            if males.allIt(it.preferences.len() == dim):
                if females.allIt(it.preferences.len() == dim):
                    result = some[Population](Population(males: males.toSeq(),
                            females: females.toSeq()))
    
    proc engage(male, female: var Spouse) =
        male.engagedTo = some[ref Person](female.base)
        female.engagedTo = some[ref Person](male.base)
    
    proc solve(population: var Population): Option[void] =
        for male in population.males:
            for female in population.females:
                let prefersMore = female.prefersMoreThanCurrent(male.base)
                if prefersMore.isNone():
                    return result
                elif prefersMore.unsafeGet():
                    engage(male, female)
    
    
    Run
    
    
    /home/u98982887/proj/cdsan/src/cdsan/stable_matching.nim(63, 23) Error: 
type mismatch: got <ref Spouse, ref Spouse>
    but expected one of:
    proc engage(male, female: var Spouse)
      first type mismatch at position: 1
      required type for male: var Spouse
      but expression 'male' is of type: ref Spouse
    
    expression: engage(male, female)
           Tip: 1 messages have been suppressed, use --verbose to show them.
         Error: Execution failed with exit code 1
            ... Command: "/home/u98982887/.nimble/bin/nim" c --noNimblePath 
-d:NimblePkgVersion=0.1.0 "-r" "--path:."  
"/home/u98982887/proj/cdsan/tests/test1"
    
    
    Run