Swift SingleValueEncodingContainer

A SingleValueEncodingContainer protocol is a component of Swift’s encoding system, designed for encoding single, non-collection values. It is particularly useful within the encode(to:) method of the Encodable protocol, enabling types to encode themselves as single values without keys.

Syntax

A type that needs to encode a single value will conform to Encodable and implement the required encode(to:) method. Within this method, the type can access a SingleValueEncodingContainer from the provided Encoder to encode its value.

struct SomeValue: Encodable {
  var value: SomeType
  func encode(to encoder: Encoder) throws {
    var container = encoder.singleValueContainer()
    try container.encode(value)
  }
}

• SomeValue struct conforms to Encodableenabling it to encode the value property.
• The singleValueContainer() method is called on the encoder to obtain a SingleValueEncodingContainer.
• The encode(_:) method is called on the container to encode the value.

Example

In the following example, an int value is encoded using SingleValueEncodingContainer:

import Foundation
struct SingleInteger: Encodable {
    let value: Int
    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(value)
    }
}
let intValue = SingleInteger(value: 42)
let encoder = JSONEncoder()
let jsonData = try? encoder.encode(intValue)
let jsonString = String(data: jsonData!, encoding: .utf8)!
print(jsonString)

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This example defines a struct SingleInteger with a value that conforms to Encodable. Within encode(to:), an Encoder is used to obtain a SingleValueEncodingContainer. The integer value is then encoded into this container. An instance of JSONEncoder takes the SingleInteger instance and encodes it into JSON data. The JSON data is then turned into a string using UTF-8 encoding for printing.

The output will display a single number in JSON format:

42

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