Formatting numbers in a String

Why is this acceptable:

Text("$\(item.price, specifier: "%.2f")")

but this isn’t:

let formattedPrice = "$\(item.price, specifier: "%.2f")"

The error I get is “Extra argument ‘specifier’ in call”

Isn’t specifier an argument to the String interpolation, rather than to the Text function?

It’s because Text in your first example is interpreted by the compiler as using this initializer:

init(_ key: LocalizedStringKey, tableName: String? = nil, bundle: Bundle? = nil, comment: StaticString? = nil)

LocalizedStringKey has as part of its conformance to ExpressibleByStringLiteral this method:

mutating func appendInterpolation<T>(_ value: T, specifier: String) where T : _FormatSpecifiable

Note the specifier parameter.

If you look at the docs for String, however, you’ll see that it has no such version of appendInterpolation so you cannot use a specifier parameter with just a string.

You can either extend String.StringInerpolation with an appropriate appendInterpolation method or you can format the string yourself. Something like this would work:

let formattedPrice = String(format: "%.2f", item.price)




Thank you. Your second, much simpler, suggestion worked perfectly.