Go backward to Declaration and Variable Parameters Go up to Top Go forward to Name Equivalence

Type Equivalence

Type attributes must match.

• Problem with type structures:
  • class R = record var X: int, var Y: int end;
    var E: R,
    var F: record var X: int, var Y: int end,
    var G: record var Y: int, var X: int end,
    proc P(Q: {X: intloc, Y: intloc}) = ...
• Structural type equivalence:
  • All have same type attribtute.
  • E, F, G can bind to Q.
  • Current typing rules.
• Name (occurence) equivalence:
  • Each class definition names new type.
  • Type structures used in place of type attributes.
  • proc P(Q: R) = ...
  • Only E can bind to Q!