Open Radar

 
Summary:
The interface for StringInterpolationConvertible provides no distinction between components of the literal format string and interpolation components whose type is String.

struct Example: StringInterpolationConvertible
{
    init(stringInterpolation strings: Example...) { ... }
    
    init<T>(stringInterpolationSegment expr: T) {
        // General case, specialized below
    }
    init(stringInterpolationSegment expr: Int) {
        // This component is an Int
    }
    init(stringInterpolationSegment expr: String) {
        // This component is EITHER a literal OR a String-typed interpolation segment?
        // This initializer will be called 3 times for the example below.
    }
}

let x = "def"
let thing: Example = "abc\(x)ghi"

Steps to Reproduce:


Expected Results:
There should be some way (an appropriate specialization, or another initializer in the protocol) to distinguish components of the interpolation literal from string values, to allow completely custom string-interpolation processing.

Actual Results:
The same specialization is used for the surrounding string literal and String-typed interpolation segments.