How to use for exponents using @infix func ( )?

Question

I want to use ** to overload an exponent function. I works if I use something like "^" but the python way of doing is ** and I would like to use that with Swift. Any way to do that?

error: Operator implementation without matching operator declaration

@infix func ** (num: Double, power: Double) -> Double{
    return pow(num, power)
}

println(8.0**3.0) // Does not work

Are you sure `^` works as intended? I've only got it to act as an addition: `println(1^2) == 3` — vol7ron, Jun 10 '14 at 04:45
@vol7ron `^` is the Bitwise XOR Operator. `1^2` is just coincidentally equal to `1+2`. Please see [The Swift Programming Language](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language), Language Guide -> Advanced Operators -> Bitwise XOR Operator. — Lensflare, Jun 26 '14 at 17:06
@Lensflare: I was speaking of Python, where `^` does not act as an exponent. I think I was wrong and misread the question, which suggests that he could overload `^` in Swift to act as a caret, but he wanted to use `**`, which was not working when trying to overload. — vol7ron, Jun 26 '14 at 19:52
You need to use Jamie's answer to tell the compiler what function name you want to use. — Chéyo, Jun 28 '14 at 15:30

Jamie Forrest · Accepted Answer · 2017-01-11T15:14:48.430

36

You need to declare the operator before defining the function, as follows:

In Swift 2:

import Darwin

infix operator ** {}

func ** (num: Double, power: Double) -> Double {
    return pow(num, power)
}

println(8.0 ** 3.0) // works

In Swift 3:

import Darwin

infix operator **

func ** (num: Double, power: Double) -> Double {
    return pow(num, power)
}

print(8.0 ** 3.0) // works

edited Jan 11 '17 at 15:14

answered Jun 06 '14 at 15:00

Jamie Forrest

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1

As of beta 6 it must be written `infix operator ** {}`. – Klaas Aug 21 '14 at 23:07
1

Thanks @Klaas, I updated the answer for Xcode 6 beta 6. – Jamie Forrest Aug 22 '14 at 16:19
1

Swift3: ``infix operator **`` <--curly braces not needed – Sentry.co Jan 10 '17 at 15:41
1

Thanks @GitSyncApp, I updated the answer with Swift 3 code as well. – Jamie Forrest Jan 11 '17 at 15:17

score 4 · Answer 2 · answered Jan 28 '15 at 22:45

To make sure that ** is executed before neighboring * or /, you'd better set a precedence.

infix operator ** { associativity left precedence 160 }

As http://nshipster.com/swift-operators/ shows, the exponentiative operators have 160 precedence, like << and >> bitwise shift operators do.

How to use ** for exponents using @infix func **( )?

2 Answers2

How to use for exponents using @infix func ( )?