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Structural equality #29

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lcnr opened this issue Mar 23, 2022 · 0 comments
Open

Structural equality #29

lcnr opened this issue Mar 23, 2022 · 0 comments
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A-param-types Const parameter types A-unification Unifying constants in the type system C-design-docs Category: This is part of our design documentation K-behavior Document Kind: regarding user visible behavior K-impl Document Kind: regarding implementation P-necessary Priority: will be needed at some point S-active

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lcnr commented Mar 23, 2022 •
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What is this

This is a design document for const generics. Any discussions about its content should be on zulip. The conclusions of these discussions should then be edited back into this issue. Please do not post any comments directly in this issue.

Content

Structural equality describes what is necessary for two constants to be considered equal.
The lower bound is that we at least consider constants equal to themselves, while we must not consider two constants to be equal if their differences can be observed in any way during CTFE. Types for which this cannot be guaranteed must not be used as const parameter types.

TODO: explore what exactly this means, reasoning about references and what not, strongly related to #24. Requires us to find a solution for #20

Using the above definition of structural equality, we ended up with a better representation for constants used in the type system, valtrees.

TODO: explain valtrees
@lcnr lcnr added C-design-docs Category: This is part of our design documentation K-impl Document Kind: regarding implementation P-necessary Priority: will be needed at some point S-active A-param-types Const parameter types A-unification Unifying constants in the type system labels Mar 23, 2022
@rust-lang rust-lang locked and limited conversation to collaborators Mar 23, 2022
@lcnr lcnr changed the title Using valtrees Structural equality Mar 23, 2022
@lcnr lcnr added the K-behavior Document Kind: regarding user visible behavior label Mar 23, 2022
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A-param-types Const parameter types A-unification Unifying constants in the type system C-design-docs Category: This is part of our design documentation K-behavior Document Kind: regarding user visible behavior K-impl Document Kind: regarding implementation P-necessary Priority: will be needed at some point S-active
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