The example is, interestingly possible in TypeScript, at a very cheap cost function modifiesValField(struct: {val: number}) { struct.val = 0; } Struct

The example is, interestingly possible in TypeScript, at a very cheap cost function modifiesValField(struct: {val: number}) { struct.val = 0; } Structural types and inline interfaces (or as I like to call them inyourfaces) are pretty cool. But I do get your point - although type systems have gotten much less annoying, its not like they're perfect.