I was writing some code that would allow transformations of values as part of
an expression, and I came across a strange error:
/// Returns the operand after a given transformation.
///
/// Example: `let newRect = myRect << { $0.origin.x += 3 }`
func << <T> (given: T, transformation: (inout T) -> ()) -> T
{
var result = given
transformation(&result)
return result
}
let volume = component.volume << { $0.ranges.z.width = 0 } // Error:
Expression type () is ambiguous without more context.
let volume = component.volume << { $0.ranges.z.width = 0; return () } // Error:
Cannot assign to property: ‘$0’ is immutable.
let volume = component.volume << { (x: inout SCNBoxVolume) in x.ranges.z.width
= 0 } // Succeeds!
Obviously, this code could easily create a var for volume and mutate it, but it
doesn’t solve my problem. Am I misunderstanding how this could work? This is
the only overload of << that accepts a closure, and even the code completion
recognizes that $0 is a SCNBoxVolume. It’s just strange that the compiler
won’t recognize $0 as an inout parameter off the bat.
Is this a bug, or a design choice?
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