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The attached code sample causes the following error on Swift 3 on Xcode 8.0 (8A218a)

Playground execution failed: error: InfixOperatorBug.playground:30:23: error: cannot assign value of type 'String' to type 'String!'
output = "test" --> 2 ~ 1
         ~~~~~~~~~~~~~^~~
                          as String!

Steps to Reproduce:
1. Run the sample playground
2. Observe error on compilation

Expected Results:
Code should compile, output "test-->2~1"
Actual Results:
Error:
Playground execution failed: error: InfixOperatorBug.playground:30:23: error: cannot assign value of type 'String' to type 'String!'
output = "test" --> 2 ~ 1
         ~~~~~~~~~~~~~^~~
                          as String!

Version:
Xcode 8.0 (8A218a), macOS Sierra 10.12 (16A323)

Notes:
Related issue: Changing output (line 35) from "let output: String!" to "let output: String" causes an ambiguous error when it should not.

Playground execution failed: error: InfixOperatorBug.playground:30:23: error: ambiguous reference to member '~'
output = "test" --> 2 ~ 1
                      ^

InfixOperatorBug.playground:5:6: note: found this candidate
func ~ (lhs: String, rhs: Int) -> String {
     ^

InfixOperatorBug.playground:9:6: note: found this candidate
func ~ (lhs: NSData, rhs: NSData) -> NSData {

code:

import Cocoa

// MARK: ~

precedencegroup TildePriorityPrecedence {
    higherThan: AssignmentPrecedence
}

infix operator ~: TildePriorityPrecedence

func ~ (lhs: String, rhs: Int) -> String {
    return "\(lhs)~\(rhs)"
}

func ~ (lhs: NSData, rhs: NSData) -> NSData {
    return NSData()
}

// MARK: -->

precedencegroup ArrowPriorityPrecedence {
    higherThan: TildePriorityPrecedence
}

infix operator -->: ArrowPriorityPrecedence

func -->(lhs: String, rhs: Float) -> String {
    return "\(lhs)-->\(rhs)"
}

func -->(lhs: CGColor, rhs: CGColor) -> CGColor {
    return CGColor.black
}

let output: String
output = "test" --> 2 ~ 1
print(output)