Impose a lone attribute to be empty in Alloy -


i wondering if there's way, in fact, force attribute of signature empty. tried way seems not work:

sig c {  myattribute: lone type }

sig type { att1: int att2: ..... etc.. }

fact {     c: c|          (my condition)          <=>         (             no c.myattribute         ) }

as can think defing structure abstract signature way:

abstract sig generaltype {} 1 sig empty extends generaltype {} sig notempty extends generaltype {...arguments (att1,2....}

the existing code should work given right my condition. (wmeyer indeed correct in suggesting that.)

you can test constraint make sure behaving expect:

sig type { }  sig c {     myattribute: lone type }  fact {     c: c | no c.myattribute }  run { } 5  check {     c: c | no c.myattribute } 5

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