[swift-users] KeyedDecodingContainerProtocol decode methods non-mutating?

[Brent Royal-Gordon]

> On Dec 28, 2017, at 1:57 PM, Ingo Maier via swift-users <swift-users at 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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