Add CPT::try_alloc_map_value #3207
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| /// let planes_trie_u8: CodePointTrie<u8> = planes::get_planes_trie(); | ||
| /// let planes_trie_u16: CodePointTrie<u16> = planes_trie_u8 | ||
| /// .try_alloc_map_value(TryFrom::try_from) | ||
| /// .expect("infallible"); |
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If rust-lang/rust#61695 ever gets stabilized then we won't need to .expect("infallible") any more
| /// | ||
| /// let planes_trie_u8: CodePointTrie<u8> = planes::get_planes_trie(); | ||
| /// let planes_trie_u16: CodePointTrie<u16> = planes_trie_u8 | ||
| /// .try_alloc_map_value(TryFrom::try_from) |
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suggestion: use different .map() function to make type width expansion more obvious
Could you replace the function with the cube function |x| x * x * x? (the square function would suffice since the 17th plane => 16 => 16^2 > u8:MAX, but x^3 is more obvious)
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I think the use case of widening the trie is also valid, so we don't need a special map.
| /// use icu_collections::codepointtrie::CodePointTrie; | ||
| /// use icu_collections::codepointtrie::planes; | ||
| /// use core::convert::Infallible; | ||
| /// | ||
| /// let planes_trie_u8: CodePointTrie<u8> = planes::get_planes_trie(); | ||
| /// let planes_trie_u16: CodePointTrie<u16> = planes_trie_u8 | ||
| /// .try_alloc_map_value(TryFrom::try_from) | ||
| /// .expect("infallible"); | ||
| /// | ||
| /// assert_eq!(planes_trie_u16.get32(0x30000), 3); |
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totally optional. this is what i was thinking of in the previous comment. i wanted to show a x^3 function, but i wasn't sure what the Error type would look like for that.
| /// use icu_collections::codepointtrie::CodePointTrie; | |
| /// use icu_collections::codepointtrie::planes; | |
| /// use core::convert::Infallible; | |
| /// | |
| /// let planes_trie_u8: CodePointTrie<u8> = planes::get_planes_trie(); | |
| /// let planes_trie_u16: CodePointTrie<u16> = planes_trie_u8 | |
| /// .try_alloc_map_value(TryFrom::try_from) | |
| /// .expect("infallible"); | |
| /// | |
| /// assert_eq!(planes_trie_u16.get32(0x30000), 3); | |
| /// use icu_collections::codepointtrie::CodePointTrie; | |
| /// use icu_collections::codepointtrie::planes; | |
| /// use core::convert::Infallible; | |
| /// | |
| /// fn try_square(x: u8) -> Result<u16, Infallible> { | |
| /// let y = x as u16; | |
| /// Ok(y * y) | |
| /// } | |
| /// | |
| /// let planes_trie_u8: CodePointTrie<u8> = planes::get_planes_trie(); | |
| /// let planes_trie_u16: CodePointTrie<u16> = planes_trie_u8 | |
| /// .try_alloc_map_value(try_square) | |
| /// .expect("infallible"); | |
| /// | |
| /// assert_eq!(planes_trie_u8.get32(0x10_0000), 16); | |
| /// assert_eq!(planes_trie_u16.get32(0x10_0000), 256); |
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Yep; actually the square function could have an error condition in the case of overflow. It could be written with checked_mul.
I'm going to merge the PR as-is but may follow up with this.
| P: TrieValue, | ||
| { | ||
| let error_converted = f(self.error_value)?; | ||
| let converted_data = self.data.iter().map(f).collect::<Result<ZeroVec<P>, E>>()?; |
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I didn't realize transforming CPTs was so straightforward!
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Yeah, for CodePointTrie it is easy but not CharsTrie :)
#2833