// DefaultStringInterpolationExtensions.swift - Copyright 2024 SwifterSwift
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public extension DefaultStringInterpolation {
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/// SwifterSwift: Interpolates the given value's textual representation
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/// into the string literal being created if the value is not `nil` and the
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/// optional predicate returns `true`, otherwise append a placeholder.
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///
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/// Do not call this method directly. It is used by the compiler when
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/// interpreting string interpolations. Instead, use string
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/// interpolation to create a new string by including values, literals,
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/// variables, or expressions enclosed in parentheses, prefixed by a
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/// backslash (`\(`...`, placeholder: `...`)`).
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///
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/// var token: Int? = nil
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/// print("\(token, placeholder: "-")")
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/// // Prints "-"
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/// token = 0
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/// print("\(token, placeholder: "-")")
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/// // Prints "0"
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/// print("\(token, placeholder: "-", where: { $0 > 0} )")
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/// // Prints "-"
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///
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/// - Parameters:
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/// - value: The values, literals, variables, or expressions to be interpolated.
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/// - placeholder: The string that displays when `value` is `nil`.
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/// - predicate: A closure that takes unwrapped `value` as its argument and returns `true` if the `value`'s
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/// textual representation should be interpolated into the string literal or `false` if the
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/// `placeholder` should be interpolated into the string literal. You can use a `nil` value for
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/// this parameter.
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mutating func appendInterpolation<T>(_ value: T?,
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placeholder: @autoclosure () -> String,
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where predicate: ((T) throws -> Bool)? = nil) rethrows {
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switch value {
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case let .some(value) where try predicate?(value) != false:
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appendInterpolation(value)
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default:
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appendInterpolation(placeholder())
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}
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}
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}
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