Alphanumeric samples bytes instead of chars
#1012
Conversation
Sampling a random alphanumeric string by collecting chars (that are known to be ASCII) into a String involves re-allocation as String is encoding to UTF-8, via the example:
```rust
let chars: String = iter::repeat(())
.map(|()| rng.sample(Alphanumeric))
.take(7)
.collect();
```
I wanted to get rid of the clearly unnecessary re-allocations in my applications, so I needed to be able to access to the ASCII characters as simple bytes. It seems like that was already what was going on inside Alphanumeric however, it was just internal.
This PR changes the `Distribution<char>` impl to provide `u8`s (which it generates internally) instead, and implements the previous `Distribution<char>` using it. One could then, for example, do this:
```rust
let mut rng = thread_rng();
let bytes = (0..7).map(|_| rng.sample(ByteAlphanumeric)).collect();
let chars = unsafe { String::from_utf8_unchecked(bytes) };
```
The corresponds more closely to the internally used types and can be easily converted to a `char` via `From` and `Into`, while being more flexible to use. This is a breaking change.
| @@ -249,7 +250,7 @@ mod tests { | |||
| '\u{ed692}', | |||
| '\u{35888}', | |||
| ]); | |||
| test_samples(&Alphanumeric, 'a', &['h', 'm', 'e', '3', 'M']); | |||
| test_samples(&Alphanumeric, 0, &[104, 109, 101, 51, 77]); | |||
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Now we need .map(..) for distributions?
Possible I think, and in a way it makes sense. What do you think?
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Now we need .map(..) for distributions?
How do you mean that? You need that if you want char, but I think that makes sense, because the conversion from u8 to char is trivial, but the other direction is not. I think it makes more sense to see Alphanumeric as a distribution of bytes, because this type is more narrow, and it's unfortunate to throw away that compile-time knowledge by forcing a conversion to char.
If you prefer, we can also use this for the test:
| test_samples(&Alphanumeric, 0, &[104, 109, 101, 51, 77]); | |
| test_samples(&Alphanumeric, b'a', &[b'h', b'm', b'e', b'3', b'M']); |
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(Edit: start again.)
The point is that here you could replace &Alphanumeric with &Alphanumeric.map(char::from) and keep the other args to test_samples as chars. Of course that doesn't matter for this test, but may be mildly useful elsewhere — though maybe not often, since we can already do Alphanumeric.sample_iter(rng).map(char::from).
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At this point, we might as well implement Iterator for distributions, no?
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We do: the .sample_iter(rng) method. The RNG has to be attached somehow.
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I think it is preferable to convert the distribution into an iterator for such cases. This also supports all the other Iterator methods, without adding more API.
Includes and thus closes #935.