CODEWITHSUNDEEP
swift
Bill
Bill

Reputation: 45408

'Ambiguous reference' when using joinWithSeparator to intersperse into array

I'm trying to use joinWithSeparator to insert a separator element between the elements of an array. Based on the documentation, I should be able to do:

[1, 2, 3].joinWithSeparator([0])

to get:

[1, 0, 2, 0, 3]

Instead, I get:

repl.swift:3:11: error: type of expression is ambiguous without more context
[1, 2, 3].joinWithSeparator([0])

How can I do this?

Upvotes: 1

Views: 632

Answers (2)

kennytm
kennytm

Reputation: 523214

joinWithSeparator does not work like this. The input should be a sequence of sequence i.e.

// swift 2:
[[1], [2], [3]].joinWithSeparator([0])
// a lazy sequence that would give `[1, 0, 2, 0, 3]`.

// swift 3:
[[1], [2], [3]].joined(separator: [0])

You could also intersperse by flatMap and then drop the last separator:

// swift 2 and 3:
[1, 2, 3].flatMap { [$0, 0] }.dropLast()

Upvotes: 4

Sulthan
Sulthan

Reputation: 130092

See the example in the generated Swift header:

extension SequenceType where Generator.Element : SequenceType {
    /// Returns a view, whose elements are the result of interposing a given
    /// `separator` between the elements of the sequence `self`.
    ///
    /// For example,
    /// `[[1, 2, 3], [4, 5, 6], [7, 8, 9]].joinWithSeparator([-1, -2])`
    /// yields `[1, 2, 3, -1, -2, 4, 5, 6, -1, -2, 7, 8, 9]`.
    @warn_unused_result
    public func joinWithSeparator<Separator : SequenceType where Separator.Generator.Element == Generator.Element.Generator.Element>(separator: Separator) -> JoinSequence<Self>
}

If you think about how it works on an array of String, it's exactly the same.

Upvotes: 0

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