type systems

Must-Knows - Fundamentals - Type systems

• Type-checking is answering a question about type equivalence, e.g. x = y, "Is the value that x holds equivalent to what y wants to hold?"
• In Static languages (aka "strong-typed"), type-checking is performed at compile time; e.g. C#, TypeScript
• In Dynamic languages (aka "weak-typed"), type-checking is performed at runtime; e.g. JavaScript
• In *Nominal languages, *everything is about what is the name of your class; e.g. In Java, myCar is considered a Car only if its class is named Car
• *Structural languages just care about shape; e.g. In TypeScript, myCar is considered a Car if it has the same properties than Car and its member's types can hold
• Duck typing: When the language passes the "duck test", it's considered a duck-typed lang, like JavaScript; Duck-typed lang = Dynamic + Structural typed lang

  If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck