New if let shorthand for optional binding
Table of Contents
In Swift 5.7 (Xcode 14), there is a new shorthand syntax for Optional binding[1].
Here is how we do optional binding before Swift 5.7
let foo: String? = "optional string"
if let foo = foo {
// foo contains a value
}
The new if-let
shorthand is a syntax for shadowing[2] an existing optional variable, which is a very common pattern.
We no longer need right-hand expression (= foo
).
let foo: String? = "optional string"
if let foo { // no longer need = foo
// foo contains a value
}
What is the problem with the current optional binding
It is a good practice to name our variable as descriptive as possible. This might lead to lengthy variable names.
let productListResponse: Array<Product>? = ...
let productNameLabel: UILabel? = ...
if let productNameLabel = productNameLabel,
let productListResponse = productListResponse,
productListResponse.count > 0 {
...
}
The problems with a long variable name and optional binding are:
- Redundancy. We have to repeat our lengthy variable name without much value out of it.
- Hard to read. The code becomes verbose and difficult to read.
- This might lead to shorter, less descriptive names for the unwrapped variables.
Using a shorter, less descriptive name for the unwrapped variables is a workaround that we used for this problem before Swift 5.7.
let productListResponse: Array<Product>? = ...
let productNameLabel: UILabel? = ...
if let label = productNameLabel,
let response = productListResponse,
response.count > 0 {
}
Optional is a core of Swift language. Having to do optional binding every day might make us unconsciously name every variable shorter.
let response: Array<Product>? = ...
let label: UILabel? = ...
if let label = label,
let response = response,
response.count > 0 {
}
This small problem led to reduction in the clarity of our codebase.
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What is the benefit of if-let shorthand
Instead of encouraging short variable names, the new shorthand allows descriptive variable names while maintaining readability.
The new if-let
shorthand lets us omit the right-hand expression, which makes our code shorter without losing its function.
let productListResponse: Array<Product>? = ...
let productNameLabel: UILabel? = ...
if let productNameLabel,
let productListResponse,
productListResponse.count > 0 {
}
The compiler automatically shadows the existing variable with the same name.
The above code is transformed into this by the compiler.
if let productNameLabel = productNameLabel,
let productListResponse = productListResponse,
productListResponse.count > 0 {
}
This new syntax applies to all places where we normally use optional binding.
if let foo { ... }
if var foo { ... }
else if let foo { ... }
else if var foo { ... }
guard let foo else { ... }
guard var foo else { ... }
while let foo { ... }
while var foo { ... }
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Conclusion
The new if-let
shorthand is one of the small changes that I think can make a nice impact on our day-to-day coding habits.
You can read more detail about this change in the SE-0345 proposal.
https://docs.swift.org/swift-book/LanguageGuide/TheBasics.html#ID333 ↩︎
Variable shadowing occurs when a variable declared within a certain scope has the same name as a variable declared in an outer scope. This outer variable is said to be shadowed by the inner variable. ↩︎
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