How can I access the parent index in a nested for loop in Swift?

Question

I have the following nested for loop in Swift:

for (index,sentenceObject) in enumerate(sentenceObjectsArray) {
    let sentence = sentenceObject as Sentence
    let sentenceIndex = index
    let wordObjectsArray = sentence.words

    for (index,word) in enumerate(wordObjectsRLMArray) {
        println(sentenceIndex) // Here I would like to access the parent
                               // for loop's index.
    }
}

How can I access the parent for loop's index?

Ian MacDonald · Accepted Answer · 2015-02-18 16:04:50Z

4

Name the inner index something else, such as indexInner. Now the name index is not overshadowed and you can refer to it.

for (index,sentenceObject) in enumerate(sentenceObjectsArray) {
    let sentence = sentenceObject as Sentence
    let sentenceIndex = index
    let wordObjectsArray = sentence.words

    for (indexInner,word) in enumerate(wordObjectsRLMArray) {
        println(index) 
        // "index" here means the outer loop's "index"
    }
}

The rule is very simple: inner scopes can see everything in the outer scope unless they are overshadowed by redeclaring the same name in the inner scope. So if you want to be able to see the outer scope name, don't redeclare it in the inner scope.

edited Feb 18, 2015 at 16:04

Ian MacDonald

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answered Feb 18, 2015 at 16:01

matt

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4 Comments

matt Over a year ago

And see my Swift tutorial: apeth.com/swiftBook/ch01.html#_scope_and_lifetime

matt Over a year ago

@webmagnets Not that there was anything terribly wrong with your original solution! Quite clever, actually.

webmagnets Over a year ago

Thanks. Unfortunately I am not clever enough to know why it was clever.

matt Over a year ago

Well, having discovered that the outer index was not passing down to the inner loop, you tried to give it a synonym that would pass down to the inner loop. And you succeeded! And since index is nothing but a number, and you've no intention of mutating it or anything weird like that, your solution works.

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