I've just been trying out the new Coding protocol, and was rather surprised
when trying to implement the `encode(to encoder: Encoder)` method.
The Swift evolution proposal provides the following example code:
public func encode(to encoder: Encoder) throws {
// Generic keyed encoder gives type-safe key access: cannot encode with
keys of the wrong type.
let container = encoder.container(keyedBy: CodingKeys.self)
// The encoder is generic on the key -- free key autocompletion here.
try container.encode(latitude, forKey: .latitude)
try container.encode(longitude, forKey: .longitude)
}
Here, container is stored as a `let` value, and uses reference semantics, while
the proposal also clearly lists these `encode` methods as mutating. With the
current implementation of the proposal, the container must be stored as a
`var`, which leads to code like the following:
var container = encoder.singleValueContainer()
try container.encode(data)
This clearly wont work as expected if the container were to have value
semantics, and writing code like this feels plain wrong. Is SE-0166 really
intended to work with referrence-type encoders only?
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