Use FormatStyle to print formatted values from a Vector structure

I'm trying to use FormatStyle from Foundation to format numbers when printing a vector structure. See code below.

import Foundation

struct Vector<T> {
    var values: [T]

    subscript(item: Int) -> T {
        get { values[item] }
        set { values[item] = newValue }
    }
}

extension Vector: CustomStringConvertible {
    var description: String {
        var desc = "( "
        desc += values.map { "\($0)" }.joined(separator: "  ")
        desc += " )"
        return desc
    }
}

extension Vector {
    func formatted<F: FormatStyle>(_ style: F) -> String where F.FormatInput == T, F.FormatOutput == String {
        var desc = "( "
        desc += values.map { style.format($0) }.joined(separator: "  ")
        desc += " )"
        return desc
    }
}

In the example below, the vector contains a mix of integer and float literals. The result is a vector with a type of Vector<Double>. Since the values of the vector are inferred as Double then I expect the print output to display as decimal numbers. However, the .number formatted output seems to ignore the vector type and print the values as a mix of integers and decimals. This is fixed by explicitly providing a format style with a fraction length. So why is the .formatted(.number) method ignoring the vector type T which is Double in this example?

let vec = Vector(values: [-2, 5.5, 100, 19, 4, 8.37])
print(vec)
print(vec.formatted(.number))
print(vec.formatted(.number.precision(.fractionLength(1...))))

( -2.0  5.5  100.0  19.0  4.0  8.37 )    // correct output that uses all Double types
( -2  5.5  100  19  4  8.37 )            // wrong output that uses Int and Double types
( -2.0  5.5  100.0  19.0  4.0  8.37 )    // correct output that uses all Double types