if let ...

[Marco S Hyman]

Both of the following code bits seem to do the same thing...

if let foo = optionalFoo,
let bar = optionalBar {
// ...
}

if let foo = optionalFoo,
bar = optionalBar {
// ...
}

Is there any reason why one should be preferred over the other?

[Chris Lattner]

You *must* use the former if you want to use a boolean condition between them with a "where" clause. In the absence of a where clause, this is a style question.

IMHO, I'd use the former when wrapping the lines as you have, but use the later when both foo/bar are on the same line, e.g.:

if let foo = optionalFoo, bar = optionalBar {
// ...
}

-Chris

[Bruno Berisso]

I try it in a playground and can't find a difference. This is the code:

let op1: Any? = "test"
let op2: Any? = 4

//Version 1

//
if let a = op1 as? String, 

        b = op2 as? Int 

   where a == "test" && b > 1 {
    "work"
} else {
    "don't work"
}

//Version 2

//
if let a = op1 as? String, 

   let b = op2 as? Int 

   where a == "test" && b > 1 {
    "work"
} else {
    "don't work"
}

This always "work"

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[Jim Dovey]

The difference is when you place a `where` clause *between* the assignments, i.e. before assigning `b`:

// This is valid

if let a = op1 as? String where !a.isEmpty,

let b = op2 as? String {

// work

}

// This is not

if let a = op1 as? String where !a.isEmpty,

b = op2 as? String { // ← missing `let`

// work

}

Cheers,

-Jim

To view this discussion on the web visit https://groups.google.com/d/msgid/swift-language/CA%2BaYCtegnFFJe%3Dh4wuOx_3p_zEToKph8dzYEm7BuMzWEBOtuyQ%40mail.gmail.com.

[Marco S Hyman]

let op1: Any? = "test"

let op2: Any? = 1

if let a = op1 as? String where a == "test",
let b = op2 as? Int where b > 1 {
"work"
} else {
"don't work”
}

That will work because all conditions are true. Change op1 from “test” to
something else and “don’t work” is the result. Change opt2 from 4 to 1 and
“don’t work” is the result, etc.

Tested with Xcode 7 beta 4