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1//
2// NonConformingFloatDecodingStrategy.swift
3// URLQueryItemCoder
4//
5// Created by Kyle Hughes on 4/10/23.
6//
7
8/// The strategy to use for non-conforming floating-point values (IEEE 754 infinity and NaN).
9public enum NonConformingFloatDecodingStrategy {
10 /// Decode the values from the given representation strings.
11 case convertToString(positiveInfinity: String, negativeInfinity: String, nan: String)
12
13 /// Throw upon encountering non-conforming values.
14 ///
15 /// This is the default strategy.
16 case `throw`
17
18 // MARK: Public Static Interface
19
20 /// The default decoding strategy.
21 ///
22 /// Equals `.throw`.
23 public static let `default`: Self = .throw
24
25 // MARK: Internal Instance Interface
26
27 internal func decode<Number, PrimitiveValue>(
28 insideOf lowLevelDecoder: LowLevelDecoder<PrimitiveValue>
29 ) throws -> Number where Number: LosslessStringConvertible & FloatingPoint {
30 let singleValueContainer = try lowLevelDecoder.container.expectedSingleValueContainer(
31 at: lowLevelDecoder.codingPath
32 )
33 let stringValue = try singleValueContainer.decode(String.self)
34
35 switch self {
36 case let .convertToString(positiveInfinity, negativeInfinity, nan):
37 switch stringValue {
38 case nan:
39 return .nan
40 case negativeInfinity:
41 return -.infinity
42 case positiveInfinity:
43 return .infinity
44 default:
45 guard let doubleValue = Number(stringValue) else {
46 throw DecodingError.dataCorrupted(
47 DecodingError.Context(
48 codingPath: singleValueContainer.codingPath,
49 debugDescription: "\(Number.self) unable to be decoded from string."
50 )
51 )
52 }
53
54 return doubleValue
55 }
56 case .throw:
57 guard let doubleValue = Number(stringValue) else {
58 throw DecodingError.dataCorrupted(
59 DecodingError.Context(
60 codingPath: singleValueContainer.codingPath,
61 debugDescription: "\(Number.self) unable to be decoded from string."
62 )
63 )
64 }
65
66 guard doubleValue.isFinite else {
67 throw DecodingError.dataCorrupted(
68 DecodingError.Context(
69 codingPath: singleValueContainer.codingPath,
70 debugDescription: "Parsed floating point number does not fit in \(Number.self)."
71 )
72 )
73 }
74
75 return doubleValue
76 }
77 }
78}