JSON initialisation using variables of primitive type about generic-json-swift HOT 2 CLOSED

This is how ExpressibleByXXXLiteral (ExpressibleByDictionaryLiteral, ExpressibleByStringLiteral, …) works in Swift.

In the first case the compiler sees a variable foo of type JSON initialized by a dictionary literal. That doesn‘t typecheck directly, but then the compiler notices that the left-hand type (JSON) conforms to ExpressibleByDictionaryLiteral, and so it offers the following initializer:

init(dictionaryLiteral elements: (String, JSON)...)

And that’s how the compiler can create a value of JSON type from a dictionary. Your second case works the same way, just using the ExpressibleByStringLiteral protocol and a different initializer:

init(stringLiteral value: String)

(These all are visible in the Initialization.swift file.)

But this machinery only works for literals, not variables, and that’s why your third example won’t compile – it’s not a literal. (If the ExpressibleByXXXLiteral machinery worked for variables, too, it would be a nightmare I guess, since you could get a lot of non-obvious automatic conversions.)

Does that make sense?

from generic-json-swift.

OK, thanks for the explanation. Makes sense.

from generic-json-swift.