Learning about Swift's lack of header files

[beccadax (Becca Royal-Gordon)]

@allevato

(So it must be doing some amount of parsing for them, which would be repeated work; I don't know enough about the details of this to gauge the overhead.)

The language is quite deliberately designed to minimize the amount of work needed to understand the declarations in a file. For instance, this is part of the reason why you have to explicitly state function parameter and return types—they don’t want to need to type-check the bodies of functions in other files.