the arc of software bends towards understanding
From the files of the ECMAScript TC39 proceedings
Single export refers to a design pattern where a module identifier is overloaded to also represent a function or type inside the module. As far as I can tell, the term “single export” is not particularly widely used outside the ECMAScript TC39 committee; however, the idea shows up in other contexts, so I’m hoping to popularize this particular name (since names are powerful).
From the files of the ECMAScript TC39 proceedings
I want to talk about an interesting duality pointed out by Mark Miller between two otherwise different language features: weak maps and private symbols. Modulo implementation differences, they are the same thing!
A weak map is an ordinary associative map, with the twist that if the key for any entry becomes unreachable, then the value becomes unreachable too (though you must remember to ignore references to the key from the value itself!) Weak maps have a variety of use-cases, including memoization, where we’d like to remember results of a computation, but only if it will ever get asked for again! A weak map supports get(key) and set(key, value) operations.
If you hang out long enough with a certain crowd (in my case, it was the ECMAScript TC39 committee), you will probably hear the term membrane tossed around. And eventually, you will start to wonder, “Well, what is a membrane, anyway?”
As is the case with many clever but simple ideas, membranes were first introduced as a footnote [1] in a PhD thesis. Suppose that you are building distributed system, in which you pass references to objects between two separate nodes. If I want to pass a reference to foo in process A to process B, I can hardly just hand over an address—the memory spaces are not the same! So instead, I need to create a wrapper object wrappedFoo representing foo in B, which knows how to access the original object in A. So far so good.