Conditional Array Merge in Swift

Question

Using SwiftUI 3.0 and Swift 5.5 on Xcode 13.2, target development > iOS 15.0.0

I'm trying to merge two arrays if a condition is met, but only one if it isn't.

I have come up with this simple function:

func conditionalArrayMerge(primaryArray: [Item], secondaryArray: [Item], condition: Bool) -> [Item] {
        if condition {
            return primaryArray + secondaryArray
        } else {
            return primaryArray
        }
    }

Is this the most efficient way to do this?

I don't want to do it like this

return condition ? primaryArray + secondaryArray : primaryArray

I tried doing it like so:

return primaryArray + { condition ? secondaryArray : [] } as [Item]

But obviously, it didn't work (unless it's not obvious?)

What's the most efficient way to return an array with conditional merges?

Thank you!

"I don't want to do it like this" <- what's wrong with that way of doing it? — Sweeper
– Sweeper, Commented Mar 17, 2022 at 14:06
Because I want to see if there's an even shorter method to get the same result — Sam Chahine
– Sam Chahine, Commented Mar 17, 2022 at 14:10

David Pasztor · Accepted Answer · 2022-03-17 14:09:48Z

3

Your syntax is wrong, you need parentheses around your ternary expression, not {}.

return primaryArray + (condition ? secondaryArray : [])

answered Mar 17, 2022 at 14:09

David Pasztor

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Comments

user652038 · Accepted Answer · 2022-03-17 14:29:55Z

1

What you're looking for is a variant of reduce that is missing from the standard library.

condition.reduce(primaryArray) { $0 + secondaryArray }

public extension Bool {
  /// Modify a value if `true`.
  /// - Returns: An unmodified value, when false.
  @inlinable func reduce<Result>(
    _ resultWhenFalse: Result,
    _ makeResult: (_ resultWhenFalse: Result) throws -> Result
  ) rethrows -> Result {
    self
      ? try makeResult(resultWhenFalse)
      : resultWhenFalse
  }
}

answered Mar 17, 2022 at 14:29

user652038

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