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Debug impl for HashMap::keys should not require values to be Debug #41924

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jonhoo opened this issue May 11, 2017 · 2 comments
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Debug impl for HashMap::keys should not require values to be Debug #41924

jonhoo opened this issue May 11, 2017 · 2 comments
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E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.

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@jonhoo
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jonhoo commented May 11, 2017

#39002 landed Debug implementations for a number of derived types in collections, but imposes overly strict requirements. For example, for std::collections::hash_map::Keys:

impl<'a, K: Debug, V: Debug> Debug for Keys<'a, K, V> { /* ... */ }

Given that only the keys are printed, we should only require K: Debug, not also V: Debug (unless I'm mistaken?).
@Mark-Simulacrum Mark-Simulacrum added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Jun 22, 2017
@sfackler sfackler added the E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. label Jun 22, 2017
@sfackler
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Yep, seems overly restrictive.

@jonhoo
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jonhoo commented Jun 22, 2017

While we're on it, Values should only require V: Debug, and the same change should be applied to BTreeMap and friends.

@razielgn razielgn mentioned this issue Jun 23, 2017
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bors pushed a commit that referenced this issue Jun 24, 2017
@razielgn
Relax Debug constraints when debugging {HashMap,BTreeMap}::{Keys,Valu…
545bfcd 
…es}.

Fixed #41924.
bors added a commit that referenced this issue Jun 24, 2017
@bors
Auto merge of #42854 - razielgn:relaxed-debug-constraints-on-maps-ite…
7e76505 
…rators, r=sfackler

Relaxed Debug constraints on {HashMap,BTreeMap}::{Keys,Values}.

I has hit by this yesterday too. 😄
And I've realised that Debug for BTreeMap::{Keys,Values} wasn't formatting just keys and values respectively, but the whole map. 🤔

Fixed #41924

r? @jonhoo
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E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue.
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