• related to programming.subtyping
• types
  • covariant : (co aka joint) only in same direction
  • Contravariant : (contra aka negative) only in opposite direction
  • Bivariant : (bi aka both) both co and contra.
  • Invariant : if the types aren't exactly the same then they are incompatible.

Lookup

• https://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science)
• https://basarat.gitbook.io/typescript/type-system/type-compatibility#variance
• Typescript example
• What are covariance and contravariance?