Hands-On Software Engineering with Golang

Liskov substitution

The third principle from SOLID that we will be exploring is the Liskov substitution principle (LSP). It was introduced by Barbara Liskov in 1987 while delivering a keynote session at the Object-Oriented Programming Systems, Languages, and Applications (OOPSLA) conference ^[22]. The formal definition of LSP is as follows:

If, for each object, O1 of type S there is an object O2 of type T such that for all programs P defined in terms of T, the behavior of P is unchanged when O1 is substituted for O2, then S is a subtype of T.

In layman's terms, two types are substitutable if their exhibited behavior follows exactly the same contract, thereby making it impossible for callers to distinguish between them. Thinking in pure OO ...