rustc recommends specialization for type parameters inside an extern block #45092

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1. MaikKlein commented on Oct 7, 2017

   

   MaikKlein

   on Oct 7, 2017

   Last edited by MaikKlein

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   I just realized that rustc doesn't refer to the feature specialization but to 'manual' specialization.

   rustc --explain E0044

   ---

   You can't use type parameters on foreign items. Example of erroneous code:

   extern { fn some_func<T>(x: T); }
   

   To fix this, replace the type parameter with the specializations that you
   need:

   extern { fn some_func_i32(x: i32); }
   extern { fn some_func_i64(x: i64); } 
   
2. sfackler

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   A-docsArea: Documentation for any part of the project, including the compiler, standard library, and toolsArea: Documentation for any part of the project, including the compiler, standard library, and tools

   on Oct 7, 2017
3. TimNN

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   C-enhancementCategory: An issue proposing an enhancement or a PR with one.Category: An issue proposing an enhancement or a PR with one.

   on Oct 10, 2017
4. steveklabnik

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   P-mediumMedium priorityMedium priority

   on Oct 31, 2017
5. QuietMisdreavus

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   A-diagnosticsArea: Messages for errors, warnings, and lintsArea: Messages for errors, warnings, and lints

   on Oct 31, 2017
6. steveklabnik

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   T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

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   A-docsArea: Documentation for any part of the project, including the compiler, standard library, and toolsArea: Documentation for any part of the project, including the compiler, standard library, and tools

   on Jan 8, 2019
7. oli-obk

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   A-suggestion-diagnosticsArea: Suggestions generated by the compiler applied by `cargo fix`Area: Suggestions generated by the compiler applied by `cargo fix`

   E-easyCall for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue.Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue.

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   P-mediumMedium priorityMedium priority

   on May 24, 2019
8. oli-obk commented on May 24, 2019

   

   oli-obk

   on May 24, 2019

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   Diagnostics triage: just needs changing the wording to something that gives a clearer message.
9. iluuu1994 commented on Jul 25, 2019

   

   iluuu1994

   on Jul 25, 2019

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   E0044 has been reworded in #48138.

   error[E0044]: foreign items may not have type parameters
    --> src/main.rs:2:5
     |
   2 |     fn sqrt<T>(f: T) -> T;
     |     ^^^^^^^^^^^^^^^^^^^^^^ can't have type parameters
     |
     = help: use specialization instead of type parameters by replacing them with concrete types like `u32`
   

   This can be closed.
10. oli-obk

    closed this as completedon Jul 26, 2019