if let: How not to use it

Today I want to show you how you should write a code in a way that shows your true intention. I use my old code that misuse if let as an example.

When I wrote this, only God and I understood what I was doing.
Now, only God knows.

Problem

I got an optional object with an optional property.

struct User {
    let name: String
    let address: Address?
}

let user: User? = User(name: "John", address: nil)

There is a time when I need to check for the presence of an object property to treat it differently.

Without much thought, sometimes, my muscle memory will write something like this.

if let user = user, let address = user.address {
    // Some logic that use `user`, but not `address`
}

I'm in a hurry, so I ignore the Xcode warning. Many months passed by coming back to refactor my code, and I see this warning.

I follow the solution and remove it.

if let user = user {
    // Some logic that use `user`, but not `address`
}

A few minutes later, my CI failed. My UI tests failing, and I spent minutes fixing them.

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What my past self should do

Instead of abusive use of let address = user.address, I should write in a way that expresses the real intent.

... to check for the presence of an object property ...

I should write it like this.

if let user = user, user.address != nil {
    // Some logic that use `user`, but not `address`
}

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Conclusion

By using language features correctly, you do colleagues and your future self a favor. A little bit of thought at a very early stage can save you significant time in the future.