3 ms·

To be clear, I'd like all tables to throw an error on unresolved key names. And I can't think of any cases where the current behavior is necessary for any of th

To be clear, I'd like all tables to throw an error on unresolved key names. And I can't think of any cases where the current behavior is necessary for any of the features I like. I think the design decision to have unresolved names result in defining a new variable, initialized to nil, is the result of a different design goal. I'm not sure what that goal was, something about fault tolerance maybe. In practice I find this feature means I need very thorough test coverage, or a metatable, as you've noted, or a static analyzer, as others have noted. Or a combination of all the above.

kemayo 4y ago
Matter of taste, then, I think. Or of how you're thinking about the language, maybe? It's not really that they're "defining a new variable" -- absent metatables, all variables always exist, and there's not a difference between one that you've accessed and one that you haven't. Behind the scenes there might be a memory allocation difference between a variable that's never been touched and one that's been used and then set back to nil, but to the user that shouldn't really matter. I'm guessing here, but the goal is probably one of simplicity -- this means there doesn't need to be special language features around declaring variables that users need to be aware of. It ties into the article's discussion of 1-indexed arrays, as things that make sense to humans who haven't done weird things to their brains as we programmers have. (Granted, `local` is somewhat a language feature for declaring variables, so there's some compromise here.) I'd probably align it with OOP in the Lua discourse. It's something that the language doesn't provide by default because it's simpler not to... but if you want it, the language makes it pretty easy to add through metatables.
wruza 4y ago
unresolved names result in defining a new variable, initialized to nil This is not what Lua does. All table lookups return a value corresponding to a specified key, if there is a correspondence. Or simply nil, doing nothing in this case. There are no global variables per se, only a table that non-local lookups end up into. In practice I find this feature means I need very thorough test coverage, or a metatable, as you've noted, or a static analyzer, as others have noted. Or a combination of all the above. You may choose a language that fits your needs rather than trying to use something that doesn’t. E.g. I think Python more or less matches your expectations here. Lua doesn’t have to please everyone, and trying to make X out of it makes no sense neither for you nor for Lua designers, if X already exists. That said, I see this as an overdramatization. Strict metatable on globals solves the issue with “automatic global variables”. But other things like static analysis and thorough testing will be required (and require your work too) in any language to achieve the “high-horse” level of guarantees.

kemayo 4y ago

Matter of taste, then, I think. Or of how you're thinking about the language, maybe? It's not really that they're "defining a new variable" -- absent metatables, all variables always exist, and there's not a difference between one that you've accessed and one that you haven't. Behind the scenes there might be a memory allocation difference between a variable that's never been touched and one that's been used and then set back to nil, but to the user that shouldn't really matter. I'm guessing here, but the goal is probably one of simplicity -- this means there doesn't need to be special language features around declaring variables that users need to be aware of. It ties into the article's discussion of 1-indexed arrays, as things that make sense to humans who haven't done weird things to their brains as we programmers have. (Granted, `local` is somewhat a language feature for declaring variables, so there's some compromise here.) I'd probably align it with OOP in the Lua discourse. It's something that the language doesn't provide by default because it's simpler not to... but if you want it, the language makes it pretty easy to add through metatables.

wruza 4y ago

unresolved names result in defining a new variable, initialized to nil This is not what Lua does. All table lookups return a value corresponding to a specified key, if there is a correspondence. Or simply nil, doing nothing in this case. There are no global variables per se, only a table that non-local lookups end up into. In practice I find this feature means I need very thorough test coverage, or a metatable, as you've noted, or a static analyzer, as others have noted. Or a combination of all the above. You may choose a language that fits your needs rather than trying to use something that doesn’t. E.g. I think Python more or less matches your expectations here. Lua doesn’t have to please everyone, and trying to make X out of it makes no sense neither for you nor for Lua designers, if X already exists. That said, I see this as an overdramatization. Strict metatable on globals solves the issue with “automatic global variables”. But other things like static analysis and thorough testing will be required (and require your work too) in any language to achieve the “high-horse” level of guarantees.