4 ms·

I will say that I've always been uncomfortable with binding new values inside an if-statement's test. As far as syntax goes, it's a good thing that it's possib

I will say that I've always been uncomfortable with binding new values inside an if-statement's test. As far as syntax goes, it's a good thing that it's possible: I'm assuming here that in Swift every statement is an expression, which is a good thing, and such a feature naturally means that doing this sort of thing should be possible. But stylistically it just feels ugly to me. I don't know if Swift has an equivalent to either of the following, but I'd prefer either of them as a cleaner idiom: Null-coalescing a la C#: self.imageUrl = json["imageUrl"].string ?? "http://example.com/empty-avatar.png"; Pattern matching a la F#: self.imageUrl <- match json["imageUrl"].string with | Some(value) -> value | None -> "http://example.com/empty-avatar.png"

mikeash 12y ago
Both of those work in Swift too. The ?? operator exists verbatim, and the matching can be done using a switch/case statement. Unfortunately, it is not true that every Swift statement is an expression. The if/let construct is actually a special case. That means that you can't do something like: if (let x = foo) && (let y = bar) { ... Which is too bad.
drivingmenuts 12y ago
I get the binding a value inside an if statement. if (i=3*someFunctionResult()) { ... blah using i ... } makes perfect sense to me. The "let" seems unnecessary and, for lack of a better term, unpoetic. Aside from which, the use of let to define a constant in the middle of an if statement is about as wrong as you can get, in my opinion. Define your constants at the top or in another file, FFs.
- bunderbunder 12y ago
  'let' doesn't define a constant, it binds an immutable value. The semantic difference is enormous. A constant has infinite lifetime and must be known at compile time. A let-binding has limited scope and can be bound a run-time. In a language like Swift that distinguishes between mutable and immutable variables, a 'let' or 'var' is needed to indicate to the compiler what kind of of variable you're trying to create. Beyond that, it also makes for a cleaner language. Creating a special syntax for let statements that only applies inside the condition for an if-statement (and presumably also loops) just so you can avoid typing a few letters approaches PHP levels of unholy grammar pollution.

mikeash 12y ago

Both of those work in Swift too. The ?? operator exists verbatim, and the matching can be done using a switch/case statement. Unfortunately, it is not true that every Swift statement is an expression. The if/let construct is actually a special case. That means that you can't do something like: if (let x = foo) && (let y = bar) { ... Which is too bad.

drivingmenuts 12y ago

I get the binding a value inside an if statement. if (i=3*someFunctionResult()) { ... blah using i ... } makes perfect sense to me. The "let" seems unnecessary and, for lack of a better term, unpoetic. Aside from which, the use of let to define a constant in the middle of an if statement is about as wrong as you can get, in my opinion. Define your constants at the top or in another file, FFs.

bunderbunder 12y ago
'let' doesn't define a constant, it binds an immutable value. The semantic difference is enormous. A constant has infinite lifetime and must be known at compile time. A let-binding has limited scope and can be bound a run-time. In a language like Swift that distinguishes between mutable and immutable variables, a 'let' or 'var' is needed to indicate to the compiler what kind of of variable you're trying to create. Beyond that, it also makes for a cleaner language. Creating a special syntax for let statements that only applies inside the condition for an if-statement (and presumably also loops) just so you can avoid typing a few letters approaches PHP levels of unholy grammar pollution.