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Similar to 幾個 Rust std 內可能有用的小技巧
Similar to 幾個 Rust std 內可能有用的小技巧 (9)
幾個 Rust std 內可能有用的小技巧
- 2. 1 3 4 12 21 22 25 29 37 38 1. Title 2. Option 3. Option::map 4. Option::and_then 5. Result 6. Result::map 7. Result::and_then 8. Result::map_err 9. Iterator 10. Iterator::fold
- 4. map
- 5. 你可以這樣做 fnfn maybe_lenmaybe_len((ss:: OptionOption<<&&strstr>>)) ->-> OptionOption<<usizeusize>> {{ matchmatch ss {{ SomeSome((ss)) =>=> SomeSome((ss..lenlen(()))),, NoneNone =>=> NoneNone,, }} }}
- 7. map fnfn maybe_lenmaybe_len((ss:: OptionOption<<&&strstr>>)) ->-> OptionOption<<usizeusize>> {{ ss..mapmap((strstr::::lenlen)) }}
- 8. map的概念是我有 ⼀個&str ⼀個fn(&str)->usize(str::len) ⼀個Option<&str> 然後我想要 fn(Option<&str>)->Option<usize>
- 12. and_then
- 13. 你可以這樣做 fnfn parse_to_i32parse_to_i32((ss:: &&strstr)) ->-> OptionOption<<i32i32>> fnfn convert_to_u32convert_to_u32((ii:: i32i32)) ->-> OptionOption<<u32u32>> fnfn i_dont_know_whati_dont_know_what((uu:: u32u32)) ->-> OptionOption<<StringString>> fnfn homework_xhomework_x((ss:: &&strstr)) ->-> OptionOption<<StringString>> {{ letlet numbernumber == parse_to_i32parse_to_i32((ss));; ifif numbernumber..is_noneis_none(()) {{ returnreturn NoneNone;; }} letlet unsignedunsigned == convert_to_u32convert_to_u32((numbernumber..unwrapunwrap(())));; ifif unsignedunsigned..is_noneis_none(()) {{ returnreturn NoneNone;; }} i_dont_know_whati_dont_know_what((unsignedunsigned..unwrapunwrap(()))) }}
- 14. 錯...錯棚？
- 15. and_then fnfn homework_x_homework_x_((ss:: &&strstr)) ->-> OptionOption<<StringString>> {{ parse_to_i32parse_to_i32((ss)) ..and_thenand_then((convert_to_u32convert_to_u32)) ..and_thenand_then((i_dont_know_whati_dont_know_what)) }}
- 19. 看看這個？ 基本是類似的概念，只是使⽤語法糖包起來，實作也有些微不同 不過就看狀況擇⼀使⽤吧 fnfn homework_x_homework_x_((ss:: &&strstr)) ->-> OptionOption<<StringString>> {{ letlet ii == parse_to_i32parse_to_i32((ss))??;; letlet uu == convert_to_u32convert_to_u32((ii))??;; i_dont_know_whati_dont_know_what((uu)) }}
- 20. 也是可以寫成這樣啦... fnfn homework_xhomework_x((ss:: &&strstr)) ->-> OptionOption<<StringString>> {{ i_dont_know_whati_dont_know_what((convert_to_u32convert_to_u32((parse_to_i32parse_to_i32((ss))??))??)) }}
- 21. Result<T,E> 可對可錯
- 22. map
- 23. 跟Option<T>::map⼀模⼀樣 如果想要下⾯這樣的邏輯時... fnfn result_lenresult_len((ss:: ResultResult<<&&strstr,, i32i32>>)) ->-> ResultResult<<usizeusize,, i32i32>> {{ matchmatch ss {{ OkOk((ss)) =>=> OkOk((ss..lenlen(()))),, ErrErr((ee)) =>=> ErrErr((ee)),, }} }}
- 24. 你可以考慮使⽤Result<T,E>::map來取代 fnfn result_len_result_len_((ss:: ResultResult<<&&strstr,, i32i32>>)) ->-> ResultResult<<usizeusize,, i32i32>> {{ ss..mapmap((strstr::::lenlen)) }}
- 25. and_then
- 26. 跟Optional<T>::and_then⼀模⼀樣 如果想要下⾯這樣的邏輯時... fnfn parse_to_i32_rparse_to_i32_r((ss:: &&strstr)) ->-> ResultResult<<i32i32,, i32i32>> fnfn convert_to_u32_rconvert_to_u32_r((ii:: i32i32)) ->-> ResultResult<<u32u32,, i32i32>> fnfn i_dont_know_what_ri_dont_know_what_r((uu:: u32u32)) ->-> ResultResult<<StringString,, i32i32>> fnfn homework_x_rhomework_x_r((ss:: &&strstr)) ->-> ResultResult<<StringString,, i32i32>> {{ letlet numbernumber == parse_to_i32_rparse_to_i32_r((ss));; ifif letlet ErrErr((ee)) == numbernumber {{ returnreturn ErrErr((ee));; }} letlet unsignedunsigned == convert_to_u32_rconvert_to_u32_r((numbernumber..unwrapunwrap(())));; ifif letlet ErrErr((ee)) == unsignedunsigned {{ returnreturn ErrErr((ee));; }} i_dont_know_what_ri_dont_know_what_r((unsignedunsigned..unwrapunwrap(()))) }}
- 27. 你值得擁有更好的 fnfn homework_x_rhomework_x_r((ss:: &&strstr)) ->-> ResultResult<<StringString,, i32i32>> {{ parse_to_i32_rparse_to_i32_r((ss)) ..and_thenand_then((convert_to_u32_rconvert_to_u32_r)) ..and_thenand_then((i_dont_know_what_ri_dont_know_what_r)) }}
- 28. 或是這樣也Ok(沒問題) fnfn homework_x_rhomework_x_r((ss:: &&strstr)) ->-> ResultResult<<StringString,, i32i32>> {{ letlet ii == parse_to_i32_rparse_to_i32_r((ss))??;; letlet uu == convert_to_u32_rconvert_to_u32_r((ii))??;; i_dont_know_what_ri_dont_know_what_r((uu)) }} 這個就有待商榷了 fnfn homework_x_rhomework_x_r((ss:: &&strstr)) ->-> ResultResult<<StringString,, i32i32>> {{ i_dont_know_what_ri_dont_know_what_r((convert_to_u32_rconvert_to_u32_r((parse_to_i32_rparse_to_i32_r((ss))??))??)) }}
- 29. map_err
- 30. 你可以這樣做 fnfn homework_yhomework_y((ss:: &&strstr)) ->-> ResultResult<<StringString,, StringString>> {{ letlet err_to_stringerr_to_string == ||ee|| format!format!(("got error: {}""got error: {}",, ee));; letlet numbernumber == parse_to_i32_rparse_to_i32_r((ss));; ifif letlet ErrErr((ee)) == numbernumber {{ returnreturn ErrErr((err_to_stringerr_to_string((ee))));; }} letlet unsignedunsigned == convert_to_u32_rconvert_to_u32_r((numbernumber..unwrapunwrap(())));; ifif letlet ErrErr((ee)) == unsignedunsigned {{ returnreturn ErrErr((err_to_stringerr_to_string((ee))));; }} letlet whatwhat == i_dont_know_what_ri_dont_know_what_r((unsignedunsigned..unwrapunwrap(())));; ifif letlet ErrErr((ee)) == whatwhat {{ returnreturn ErrErr((err_to_stringerr_to_string((ee))));; }} OkOk((whatwhat..unwrapunwrap(()))) }}
- 32. map_err fnfn homework_yhomework_y((ss:: &&strstr)) ->-> ResultResult<<StringString,, StringString>> {{ letlet to_strto_str == ||ee|| format!format!(("got error: {}""got error: {}",, ee));; letlet numbernumber == parse_to_i32_rparse_to_i32_r((ss))..map_errmap_err((to_strto_str));; ifif letlet ErrErr((ee)) == numbernumber {{ returnreturn ErrErr((ee));; }} letlet unsignedunsigned == convert_to_u32_rconvert_to_u32_r((numbernumber..unwrapunwrap(())))..map_errmap_err((to_strto_str));; ifif letlet ErrErr((ee)) == unsignedunsigned {{ returnreturn ErrErr((ee));; }} letlet whatwhat == i_dont_know_what_ri_dont_know_what_r((unsignedunsigned..unwrapunwrap(())))..map_errmap_err((to_strto_str));; ifif letlet ErrErr((ee)) == whatwhat {{ returnreturn ErrErr((ee));; }} OkOk((whatwhat..unwrapunwrap(()))) }}
- 33. 嗯...事情看起來還是挺糟糕的
- 34. ⽤上之前學過的好⽤技巧後... fnfn homework_yhomework_y((ss:: &&strstr)) ->-> ResultResult<<StringString,, StringString>> {{ parse_to_i32_rparse_to_i32_r((ss)) ..and_thenand_then((convert_to_u32_rconvert_to_u32_r)) ..and_thenand_then((i_dont_know_what_ri_dont_know_what_r)) ..map_errmap_err((||ee|| format!format!(("got error: {}""got error: {}",, ee)))) }} 沒錯，只要多加⼀⾏map_err，就能好好的表達意圖了
- 35. 使⽤?的版本，看起來效果有限 fnfn homework_y_homework_y_((ss:: &&strstr)) ->-> ResultResult<<StringString,, StringString>> {{ letlet err_to_strerr_to_str == ||ee|| format!format!(("got error: {}""got error: {}",, ee));; letlet ii == parse_to_i32_rparse_to_i32_r((ss))..map_errmap_err((err_to_strerr_to_str))??;; letlet uu == convert_to_u32_rconvert_to_u32_r((ii))..map_errmap_err((err_to_strerr_to_str))??;; i_dont_know_what_ri_dont_know_what_r((uu))..map_errmap_err((err_to_strerr_to_str)) }}
- 37. Iterator ⼀個⼀個來
- 38. fold
- 39. 你⼀定這樣做過 fnfn sumsum((numsnums:: &&[[i32i32]])) ->-> i32i32 {{ letlet mutmut sumsum == 00;; forfor nn inin numsnums {{ sumsum +=+= nn;; }} sumsum }} 但是我們可以做的更好
- 40. 先讓我們忽略這個 fnfn sumsum((numsnums:: &&[[i32i32]])) ->-> i32i32 {{ numsnums..iteriter(())..sumsum(()) }}
- 42. ⽤剛剛的sum當作例⼦，如果使⽤fold來寫，是這樣 numsnums..iteriter(())..foldfold((00,, i32i32::::addadd)) 或是 numsnums..iteriter(())..foldfold((00,, ||accacc,, xx|| accacc ++ xx))
- 43. numsnums..iteriter(())..foldfold((00,, ||accacc,, xx|| accacc ++ xx)) ⼀連串的資料=很多i ⼀些操作=加法 最後的結果=⼀個i
- 44. fold真的不複雜 letlet numsnums == [[11,,22,,33,,44,,55]];; letlet sumsum == numsnums..iteriter(())..foldfold((00,, ||accacc,, xx|| accacc ++ xx));; 其實就是 letlet numsnums == [[11,,22,,33,,44,,55]];; letlet sumsum == ((((((((((00 ++ 11)) ++ 22)) ++ 33)) ++44)) ++ 55)) 所以我們才需要給⼀個起始值0
- 45. 為什麼要⽤fold？因為這樣可以減少許多重複的操作 繼續使⽤剛剛的例⼦，我們已經有了 i 這個型別 add(+)這個函數 ⼀連串的i 要完成sum，我們缺少的就是⼀個把他們組合起來的明確概念了
- 47. 重點是!
- 49. flat_map
- 50. 先來說說Iterator::map就好 letlet numsnums == [[11,,22,,33]];; numsnums..iteriter(())..mapmap((||ee|| ee ** ee));; // 我們可以拿到 [1, 4, 9] 的 Iterator// 我們可以拿到 [1, 4, 9] 的 Iterator [1,2,3]經過運算|e|e*e變成[1,4,9]，數量是不變的
- 51. 如果我們想要這樣做呢 [[11,,22,,33]] ->-> [[11,, 22,, 22,, 33,, 33,, 33]] 對於每個元素n，產⽣n個n 很明顯，這個並不map的⾏為，因為數量改變了
- 52. 過去我們可能會這樣做 letlet mutmut xx == VecVec::::newnew(());; forfor ii inin 11..=..=55 {{ forfor __ inin 00....ii {{ xx..pushpush((ii));; }} }} 這是個可⾏的解法，但是有個很嚴重的缺點 那就是得到的結果並不是Iterator，這表⽰所有東⻄都要乖乖算完才能 得到結果
- 53. 我們到底想要做什麼呢 [[11,,22,,33]] =>=> [[[[11]],, [[22,, 22]],, [[33,, 33,, 33]]]] // A// A =>=> [[11,, 22,, 22,, 33,, 33,, 33]] // B// B A的部分，數量是⼀樣的，這表⽰我們可以⽤map，從i 產⽣ Iterator<i > B的部分，則是要把Iterator<Iterator<i >>變成Iterator<i >
- 54. map⼤家都很熟了，就不多說 我們可以⽤iter::repeat跟take達到⽬的 fnfn repeat_nrepeat_n((nn:: u16u16)) ->-> implimpl IteratorIterator<<ItemItem == u16u16>> {{ repeatrepeat((nn))..taketake((usizeusize::::fromfrom((nn)))) }} [[11,, 22,, 33]]..iteriter(())..mapmap((repeat_nrepeat_n)) // [[1], [2, 2], [3, 3, 3]]// [[1], [2, 2], [3, 3, 3]] 這樣我們就拿到Iterator的Iterator了
- 55. B的部分，則是要把Iterator<Iterator<i >>變成Iterator<i > 太好了，Iterator::flatten就是這樣⽤的! fnfn repeat_nrepeat_n((nn:: u16u16)) ->-> implimpl IteratorIterator<<ItemItem == u16u16>> {{ repeatrepeat((nn))..taketake((usizeusize::::fromfrom((nn)))) }} [[11,, 22,, 33]]..iteriter(())..mapmap((repeat_nrepeat_n)) // [[1], [2, 2], [3, 3, 3]]// [[1], [2, 2], [3, 3, 3]] [[11,, 22,, 33]]..iteriter(())..mapmap((repeat_nrepeat_n))..flattenflatten(()) // [1, 2, 2, 3, 3, 3]// [1, 2, 2, 3, 3, 3]
- 56. 現在你知道為什麼他叫做flat_map了！ 他是計算完後，會進⾏flatten的map [[11,, 22,, 33]]..iteriter(())..flat_mapflat_map((repeat_nrepeat_n)) // [1, 2, 2, 3, 3, 3]// [1, 2, 2, 3, 3, 3] [[11,, 22,, 33]]..iteriter(())..mapmap((repeat_nrepeat_n)) // [[1], [2, 2], [3, 3, 3]]// [[1], [2, 2], [3, 3, 3]] [[11,, 22,, 33]]..iteriter(())..mapmap((repeat_nrepeat_n))..flattenflatten(()) // [1, 2, 2, 3, 3, 3]// [1, 2, 2, 3, 3, 3]
- 58. 等等...
- 59. 怪怪的 fnfn flat_mapflat_map((IterIter<<TT>>,, fnfn((TT)) ->-> IterIter<<UU>>)) ->-> IterIter<<UU>> fnfn and_thenand_then((OptionOption<<TT>>,, fnfn((TT)) ->-> OptionOption<<UU>>)) ->-> OptionOption<<UU>> fnfn and_thenand_then((ResultResult<<TT,, EE>>,, fnfn((TT)) ->-> OptionOption<<UU,, EE>>)) ->-> OptionOption<<UU,, EE>>
- 64. implFromIterator<(K,V)>forHashMap<K,V> letlet mapmap:: HashMapHashMap<<StringString,, i32i32>> == [[ (("one""one"..intointo(()),, 11)),, (("two""two"..intointo(()),, 22)),, (("the_answer""the_answer"..intointo(()),, 4242)),, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..collectcollect(());; // HashMap 內容有// HashMap 內容有 // ("one", 1),// ("one", 1), // ("two", 2)// ("two", 2) // ("the_answer", 42)// ("the_answer", 42)
- 65. implFromIterator<String>forString letlet ss:: StringString == [[ "apple > ""apple > ",, "orange > ""orange > ",, "lemon > ""lemon > ",, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..mapmap((strstr::::to_stringto_string)) ..collectcollect(());; // "apple > orange > lemon > "// "apple > orange > lemon > "
- 66. implFromIterator<Option<A>>forOption<V> whereV:FromIterator<A> letlet oo:: OptionOption<<VecVec<<i32i32>>>> == [[ SomeSome((1111)),, SomeSome((1212)),, SomeSome((2424)),, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..collectcollect(());; // Some([11, 12, 24])// Some([11, 12, 24])
- 67. implFromIterator<Option<A>>forOption<V> whereV:FromIterator<A> letlet oo:: OptionOption<<VecVec<<i32i32>>>> == [[ SomeSome((1111)),, NoneNone,, SomeSome((2424)),, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..collectcollect(());; // None// None
- 68. implFromIterator<Result<A,E>>forResult<V,E> whereV:FromIterator<A> letlet rr:: ResultResult<<VecVec<<i32i32>>,, StringString>> == [[ OkOk((1111)),, OkOk((2222)),, OkOk((2424)),, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..collectcollect(());; // Ok([11, 22, 24])// Ok([11, 22, 24])
- 69. implFromIterator<Result<A,E>>forResult<V,E> whereV:FromIterator<A> letlet rr:: ResultResult<<VecVec<<i32i32>>,, StringString>> == [[ OkOk((1111)),, ErrErr(("Error!!""Error!!"..to_stringto_string(()))),, OkOk((2424)),, ]] ..iteriter(()) ..clonedcloned(()) // 要記得這個，型別才會對// 要記得這個，型別才會對 ..collectcollect(());; // Err("Error!!")// Err("Error!!")
- 72. 你可能會這樣寫 letlet mutmut mm == HashMapHashMap::::<<i32i32,, StringString>>::::newnew(());; ifif letlet NoneNone == mm..getget((&&4242)) {{ mm..insertinsert((4242,, "the answer""the answer"..intointo(())));; }} letlet valuevalue == mm..getget((&&4242))..unwrapunwrap(());;
- 73. Entry letlet mutmut mm == HashMapHashMap::::<<i32i32,, StringString>>::::newnew(());; letlet valuevalue == mm..entryentry((4242))..or_insert_withor_insert_with((|||| "the answer""the answer"..intointo(())));;
- 76. Q&A
- 77. Thanks!