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August 29, 2015 14:16
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Extend Swift's Array#reduce behavior to provide reasonable initial values
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extension Array { | |
func deduce (initial: T? = nil, _ combine: (T, T) -> T) -> T? { | |
if let initial = initial { | |
return reduce(initial, combine: combine); | |
} | |
if count > 1 { | |
var rest = self[1..<count] | |
return rest.reduce(first!, combine: combine) | |
} else { | |
return first | |
} | |
} | |
} | |
protocol Constructable { | |
init() | |
} | |
extension String: Constructable {} | |
extension Int: Constructable {} | |
extension Array { | |
func deduce_ <U: Constructable> (initial: U = U(), _ combine: (U, T) -> U) -> U { | |
return reduce(initial, combine: combine) | |
} | |
} | |
var a = [1,2,3] | |
assert(a.reduce(0, combine: +) == 6) | |
assert(a.deduce(initial: 1, +) == 7) | |
assert(a.deduce(+) == 6) | |
assert([Int]().deduce(+) == nil) | |
assert([1].deduce(+) == 1) | |
assert(a.deduce_(initial: 1, +) == 7) | |
assert(a.deduce_(+) == 6) | |
assert([Int]().deduce_(+) == 0) // the behavior is differnt than deduce above | |
assert([1].deduce_(+) == 1) | |
var b = ["a", "b", "c"] | |
assert(b.deduce_(+) == "abc") | |
assert(b.deduce_(initial: "!", +) == "!abc") | |
assert(a.deduce_ { $0 + String($1) } == "123") | |
extension Int { | |
init(_ strValue: String) { | |
var value = strValue.toInt() | |
self.init(value ?? 0) | |
} | |
} | |
assert(["1", "2", "3", "a"].deduce_ { $0 + Int($1) } == 6) // :mindblown: |
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