Docs for implementing SeedableRng for large seeds
#381
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The failure on nightly seems unrelated. |
rand_core/src/lib.rs
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| /// pub struct MyRngSeed(pub [u8; N]); | ||
| /// | ||
| /// impl Default for MyRngSeed { ... } | ||
| /// impl AsMut<u8> for MyRngSeed { ... } |
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With just a few more lines the example can be made complete. Maybe it is worth it to do so? (and then also does not need to be ignored)
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I expanded the example to actually compile. What do you think?
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Can you use fn default() -> MyRngSeed { MyRngSeed([0u8; 64]) } instead?
rand_core/src/lib.rs
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| @@ -307,6 +329,25 @@ pub trait SeedableRng: Sized { | |||
| /// seeds it is preferable to map these to alternative constant value(s), | |||
| /// for example `0xBAD5EEDu32` or `0x0DDB1A5E5BAD5EEDu64` ("odd biases? bad | |||
| /// seed"). This is assuming only a small number of values must be rejected. | |||
| /// Alternatively, the newtype pattern can be used to make sure only valid | |||
| /// seeds can be constructed: | |||
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I don't really like this as a pattern. RNG implementations can do as they wish, but we shouldn't advertise it here i.m.o.
It is useful for generic code to have from_seed work with all simple slices. The default implementation of from_rngrelies on this, and something like from_hashablewould too.
Also, does it really work? With the AsMut implementation wouldn't it be possible to modify the newtype outside new()?
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Also, does it really work? With the AsMut implementation wouldn't it be possible to modify the newtype outside new()?
Good point! I removed the suggestion to use the newtype pattern to work around invalid seeds.
This does not work, because the seed has to implement `AsMut<[u8]>`, so any invariants enforced by the constructor can be circumvented.
rand_core/src/lib.rs
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| /// type Seed = MyRngSeed; | ||
| /// | ||
| /// fn from_seed(seed: MyRngSeed) -> MyRng { | ||
| /// MyRng(MyRngSeed) |
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Should be MyRng(seed) (reason of the CI failure)
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Looks good to me! Let's wait until @dhardy had a chance to look over it to before merging. |
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Yep, looks good! 👍 @pitdicker can you sort out the merging? |
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I restarted the Travis build. @pitdicker if you have a Travis account I think you should be able to do that too. |
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I already restarted travis, but that was not enough |
Fixes #354.