Update: with Xcode 12, we can write if let bindings without problems. This code is now valid:

if let address = library.address {
    Text(address)
}

I'll leave the post up for historical context.

Recently I was building an app that lists public libraries in my home city. In early stages, the main view was just a list view that displays the library name and address. Something like this:

As you can see, some libraries don't have an address, because of some unrelated reasons. And if the address isn't present, the name should be vertically centred in the row.

A library not having an address is translated into my data model as an optional String. Here's a simplified version of my Library model:

struct Library {
    let id: String
    let name: String
    let address: String?
}

Initial approach

If a library doesn't have an address, I won't render a Text component for it, simple as that. And the easiest way for me to do that was using an if let binding:

VStack {
    Text(library.name)
    if let address = library.address {
        Text(address)
    }
}

As it turns out, SwiftUI doesn't like this. The compiler tells us that Closure containing control flow statement cannot be used with function builder 'ViewBuilder'. I beg your pardon?

How else am I supposed to conditionally render views in my app if "control flow statement cannot be used" to build it? After a moment of panic, I tested using a normal if:

VStack {
    Text(library.name)
    if library.address != nil {
        Text(library.address!)
    }
}

And surprisingly that worked... wtf. Needless to say, I wasn't very exited with that solution, since it requires force unwrapping an optional value. I knew that there was another way.

Current solution

One of the key features of SwiftUI is that if we add a nil component to our view, it won't show up, it's just ignored. So, what's the easiest way to convert a conditional string into a conditional Text? That's right, using map.

Here we map over the possibly nil address, without needing to force unwrap it, as the closure will only be executed if there was a value in the first place. This, however, seems like a hack. But hey, It works.

VStack {
    Text(library.name)
    library.address.map { address in
        Text(address)
    }
}

Let's wait and see

As I was reading some discussions about this issue, I found out that SwiftUI builds views using a struct named ViewBuilder — remember the error I was getting before? If we peek its definition (cmd + shift + o in XCode to go to any class definition) we can clearly see that it supports if statements, but nothing more.

SwiftUI is not event a year old, and we know Apple only introduces big features once a year. So here's hoping that when the next version of SwiftUI shows up, they add if let support.