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context: WithValue documentation should discourage use of basic types #17302

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mdlayher opened this issue Sep 30, 2016 · 7 comments
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context: WithValue documentation should discourage use of basic types #17302

mdlayher opened this issue Sep 30, 2016 · 7 comments
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Documentation Issues describing a change to documentation. FrozenDueToAge Suggested Issues that may be good for new contributors looking for work to do.
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Go1.8

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@mdlayher
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mdlayher commented Sep 30, 2016 •
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Related to: #17293.

I've submitted a fix to golint to begin warning about this, but I also feel that it would be a good idea to explicitly document that only user-defined types should be used as keys in context.WithValue.

As of now, there is no such warning. The only advice given is:

The provided key must be comparable.

EDIT: I was incorrect, see: #17302 (comment).

CC @bradfitz @alandonovan
@bradfitz
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Yes, please!

@bradfitz bradfitz added this to the Go1.8 milestone Sep 30, 2016
@bradfitz bradfitz added Suggested Issues that may be good for new contributors looking for work to do. Documentation Issues describing a change to documentation. labels Sep 30, 2016
@mdlayher
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I'll submit a CL shortly.

@mdlayher
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It appears I was incorrect: https://golang.org/pkg/context/#Context

        // A key identifies a specific value in a Context. Functions that wish
        // to store values in Context typically allocate a key in a global
        // variable then use that key as the argument to context.WithValue and
        // Context.Value. A key can be any type that supports equality;
        // packages should define keys as an unexported type to avoid
        // collisions.

Should this be reiterated in the documentation for context.WithValue, or is the documentation on the context.Context interface enough?

@bradfitz
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More warnings SGTM.

@mdlayher
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CL submitted: https://go-review.googlesource.com/c/30134/.

Happy to re-phrase as needed.

@gopherbot
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CL https://golang.org/cl/30134 mentions this issue.

@bradfitz bradfitz mentioned this issue Nov 6, 2016
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@gopherbot
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CL https://golang.org/cl/33152 mentions this issue.

gopherbot pushed a commit that referenced this issue Nov 12, 2016
@bradfitz
context: document appropriate WithValue key type more
c921d8f 
Fixes #17826
Updates #17302

Change-Id: I7c1ebd965e679e7169a97e62d27ae3ede2473aa1
Reviewed-on: https://go-review.googlesource.com/33152
Reviewed-by: Ian Lance Taylor <iant@golang.org>
@golang golang locked and limited conversation to collaborators Nov 12, 2017
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