> On Dec 28, 2017, at 1:57 PM, Ingo Maier via swift-users > <swift-users@swift.org> wrote: > > Can anybody tell why the decode methods in UnkeyedDecodingContainer > are marked mutating but those in KeyedDecodingContainerProtocol and > SingleValueDecodingContainer are not? Is it a simple oversight or is > there a reason for this? It seems to me that all of them should be > mutating.
The `UnkeyedDecodingContainer.decode(_:)` methods consume values as they decode them; that is, the first call returns the first value, the second call returns the second value, etc. The ones in the other containers don't consume values; in theory, you could decode the same key twice and you should get the same value both times. So the UnkeyedDecodingContainer methods are mutating, but the other containers' methods are not. -- Brent Royal-Gordon Architechies
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