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Update const_eval.md for feature stabilization #1166

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merged 4 commits into from
Mar 8, 2022
Merged

Update const_eval.md for feature stabilization #1166

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27dabb2
Update const_eval.md for feature stabilization
eholk Feb 10, 2022
107fda2
dyn Trait types are allowed now too
eholk Feb 14, 2022
31832a3
Update does to reflect that union field access works too
eholk Mar 1, 2022
806370f
Remove 'compairing raw pointers'
eholk Mar 3, 2022
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10 changes: 3 additions & 7 deletions src/const_eval.md
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Expand Up @@ -65,8 +65,8 @@ A _const context_ is one of the following:

A _const fn_ is a function that one is permitted to call from a const context. Declaring a function
`const` has no effect on any existing uses, it only restricts the types that arguments and the
return type may use, as well as prevent various expressions from being used within it. You can freely do anything with a const function that
you can do with a regular function.
return type may use, as well as prevent various expressions from being used within it. You can freely
do anything with a const function that you can do with a regular function.

When called from a const context, the function is interpreted by the
compiler at compile time. The interpretation happens in the
Expand All @@ -84,15 +84,11 @@ slightly) different results. It is advisable to not make array lengths and enum
discriminants depend on floating point computations.


Notable features that const contexts have, but const fn haven't are:
Notable features that are allowed in const contexts but not in const functions include:

* floating point operations
* floating point values are treated just like generic parameters without trait bounds beyond
`Copy`. So you cannot do anything with them but copy/move them around.
* `dyn Trait` types
* generic bounds on generic parameters beyond `Sized`
* comparing raw pointers
* union field access

Conversely, the following are possible in a const function, but not in a const context:

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