Type systems are leaky abstractions: the case of Map.take!/2

4 days ago

Type systems in dynamic languages can restrict expressive power, illustrated by the proposed Map.take!/2 function in Elixir.
Map.take!/2 would raise an error if a key doesn't exist, unlike Map.take/2 which silently ignores missing keys.
Current type signatures for Map.take!/2 are too broad, failing to specify the exact shape of the returned map.
TypeScript's keyof operator offers a solution but has limitations, especially with dynamic key lists.
Refactoring code can lead to type system violations, showing how type systems can work against best practices.
Macros are proposed as a solution to enforce static guarantees on key lists, though they come with their own trade-offs.
The article highlights the trade-offs between language simplicity and expressiveness when adding type systems to dynamic languages.

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