Reduce into

Prefer reduce(into:_:) over reduce(_:_:) for copy-on-write types

• Identifier: reduce_into
• Enabled by default: No
• Supports autocorrection: No
• Kind: performance
• Analyzer rule: No
• Minimum Swift compiler version: 5.0.0
• Default configuration:

  Key	Value
  severity	warning

Non Triggering Examples

let foo = values.reduce(into: "abc") { $0 += "\($1)" }

values.reduce(into: Array<Int>()) { result, value in
    result.append(value)
}

let rows = violations.enumerated().reduce(into: "") { rows, indexAndViolation in
    rows.append(generateSingleRow(for: indexAndViolation.1, at: indexAndViolation.0 + 1))
}

zip(group, group.dropFirst()).reduce(into: []) { result, pair in
    result.append(pair.0 + pair.1)
}

let foo = values.reduce(into: [String: Int]()) { result, value in
    result["\(value)"] = value
}

let foo = values.reduce(into: Dictionary<String, Int>.init()) { result, value in
    result["\(value)"] = value
}

let foo = values.reduce(into: [Int](repeating: 0, count: 10)) { result, value in
    result.append(value)
}

let foo = values.reduce(MyClass()) { result, value in
    result.handleValue(value)
    return result
}

Triggering Examples

let bar = values.↓reduce("abc") { $0 + "\($1)" }

values.↓reduce(Array<Int>()) { result, value in
    result += [value]
}

[1, 2, 3].↓reduce(Set<Int>()) { acc, value in
    var result = acc
    result.insert(value)
    return result
}

let rows = violations.enumerated().↓reduce("") { rows, indexAndViolation in
    return rows + generateSingleRow(for: indexAndViolation.1, at: indexAndViolation.0 + 1)
}

zip(group, group.dropFirst()).↓reduce([]) { result, pair in
    result + [pair.0 + pair.1]
}

let foo = values.↓reduce([String: Int]()) { result, value in
    var result = result
    result["\(value)"] = value
    return result
}

let bar = values.↓reduce(Dictionary<String, Int>.init()) { result, value in
    var result = result
    result["\(value)"] = value
    return result
}

let bar = values.↓reduce([Int](repeating: 0, count: 10)) { result, value in
    return result + [value]
}

extension Data {
    var hexString: String {
        return ↓reduce("") { (output, byte) -> String in
            output + String(format: "%02x", byte)
        }
    }
}