On Fri, Nov 2, 2012 at 4:30 PM, Allen Wirfs-Brock <al...@wirfs-brock.com>wrote:
> There is no verifiable formal contract. But there can be an informal > contract. In my experience, it is very important when using a dynamic > language to recognize and try to support such informal contracts. > Well, I sort of agree. But even Ruby, as much as it owes to Smalltalk, provides same-named methods in Array and Hash with completely incompatible semantics. Hash»delete takes a key argument; Array»delete takes a value. Array»each yields values; Hash»each yields key-value pairs. I expect this is just because the operations you need from an Array vs. a Hash are really different in practice. Their abstract conceptual similarity doesn't seem to make the jump to the real world. Returning to JS: is there really an informal contract that unifies Array, Map, and strings? In the current spec, there's not a single method that works the same way across all three! The only thing that even *exists* across all three is .@@iterator(), which is no small thing. But note that Array.prototype.@@iterator yields element values, String.prototype.@@iterator yields UTF-16-encoded characters, and Map.prototype.@@iterator yields key-value pairs. A common protocol could certainly be added. For the sake of concreteness: they could all have .hasKey(k), .hasValue(v), .get(k), .size, .keys(), .values(), .items(), .forEach(f); and on mutable collections, .set(k, v), .delete(k), .clear(). But I think the aesthetic appeal of this sort of thing is way out of proportion to its practical value. -j
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