Message from JavaScript discussions

September 2017

— With static in C++, you define one or more types a function can return, and which code to use for which types of parameters. Very cool template metaprogramming. You can include multiple types in some languages, too

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Duck typing is more like checking the structure and properties of an object to see if it matches certain criteria

— "If it looks like a duck and quacks like a duck, it's a duck"

— In JS this is commonly used to validate incoming parameter objects. I wrote something that does it:

assert.props(obj, "prop" ...);

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— Very handy :D

— Non-ducktyping version of this would be: e.g. typeof parameter == 'whatever'

— Yeah

— But that's kind of bad practice in languages with duck-typing, since it means you can't easily subclass/add behaviour

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— Or instanceof or isPrototypeOf

— Complex duck typing can also validate functions, I think

— But that's more unit-testy and less production

— Well, instanceof would still work in JS:

class MyError extends SyntaxError {
new TypeError() instanceof Error // true
new MyError() instanceof Error // true

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