Lisp-kwan so C++ nsusuwso meta nhyehyɛe

Comiler Magic a ɛsono: Lisp-Style C++ Template Metaprogramming

Wɔ software nkɔsoɔ asase kɛseɛ no mu no, C++ agye din wɔ ne raw power ne adwumayɛ ho. Nanso, wɔde nhwɛsode bi a ɛkame ayɛ sɛ ɛte sɛ nea ɛyɛ ahɔho de asie ne nhyehyɛe a ɛyɛ den a ɛboaboa ano no mu: template metaprogramming (TMP). Sɛ wɔde kɔ ne ntease mu koraa a, C++ TMP fi ase te sɛ nhyehyɛe kasa a ɛyɛ adwuma wɔ n’ankasa mu, nea ɛyɛ adwuma koraa wɔ bere a wɔaboaboa ano. Nsɛdi a ɛne Lisp, nhyehyɛe kasa a akyɛ na ɛwɔ nkɛntɛnso sen biara no mu biako no yɛ nwonwa na emu dɔ. Saa kwan yi ma wɔn a wɔyɛ no tumi yi kɔmputa ne nteaseɛ a ɛyɛ den fi runtime so kɔ compile-time so, na ɛyɛ code a ɛyɛ adwuma yie na ɛyɛ type-safe. Saa Lisp-style kwan yi nteaseɛ yɛ ade titire a ɛbɛma yɛabue abstraction level foforɔ, nnyinasosɛm a yɛbu no sɛ ɛsom boɔ kɛseɛ wɔ Mewayz berɛ a yɛresi adwumayɛ nhyehyɛeɛ a ɛyɛ den, modular.

Akwanhyia Dwumadie Kasa a Ɛwɔ C++

Wɔyɛɛ C++ nsusuiɛ mfitiaseɛ no maa type substitution a ɛnyɛ den, te sɛ `List` anaa `List` a wɔbɛbɔ. Nanso, C++ gyinapɛn no, wɔ ne nyinaa akyi di mu no, ɛde Turing-kasa ketewa a edi mũ bae wɔ akwanhyia mu. Wei kyerɛ sɛ, wɔ nsusuiɛ mu no, akontabuo biara a dwumadie bi bɛtumi ayɛ no nso, C++ compiler no nso bɛtumi ayɛ wɔ template instantiation dwumadie no mu. Saa tumi yi a wohuu no ma wɔwoo template metaprogramming. Wohui sɛ ɛdenam template specialization, recursion, ne template parameters a obi de di dwuma so no, obetumi akyerɛw program ahorow a compiler no yɛ bere a ɔresi wo application no. Saa compile-time "kasa" yi nni nsakrae biara wɔ atetesɛm ntease mu; ne tebea no wɔ template parameters no ankasa mu, na ne control structures no gyina recursion ne conditional compilation so.

Adwene a Ɛyɛ Dwumadi, a ɛte sɛ Lisp a Wogye tom

Sɛ obi bɛkyerɛw template metaprograms yie a, ɛsɛ sɛ ɔfa dwumadie nhyehyɛeɛ adwene, te sɛ Lisp programmer. Tebea anaa loop ahorow biara nni hɔ a ɛsakra wɔ ntease a wɔde di dwuma wɔ tete mmere mu no mu. Mmom no, biribiara nam recursion ne manipulation of types ne compile-time constants so na ɛba. Susuw nhwɛso tiawa bi ho hwɛ: factorial a wobu akontaa. Wɔ Lisp mu no, wobɛtumi de recursive function adi dwuma. Wɔ C++ TMP mu no, ɔkwan no di nsɛ wɔ ɔkwan a ɛyɛ nwonwa so, nanso ɛne ahorow ne botae ahorow yɛ adwuma.

• Data a Ɛnsakra: Sɛnea ɛte wɔ Lisp mu no, data a ɛwɔ TMP mu no ntumi nsakra. Sɛ wɔde template parameter bi si hɔ wie a, wɔrentumi nsakra; wobɛtumi ayɛ "instances" foforɔ a ɛwɔ parameter ahodoɔ nko ara.
• Recursion as Iteration: Esiane sɛ `for` anaa `while` loops nni hɔ nti, recursion ne ɔkwan titiriw a wɔfa so yɛ adwuma mpɛn pii. Template bi de parameters a wɔayɛ no foforɔ frɛ ne ho kɔsi sɛ wɔbɛduru base case (ɛnam template specialization so).
• Manipulating Types, Not Just Values: TMP afã a tumi wom sen biara ne sɛnea etumi de types bu akontaa. Wubetumi ayɛ type lists, ahwɛ type properties, na woapaw types a egyina tebea horow so, ama generic programming techniques a tumi wom ayɛ adwuma.

Saa nhwɛsoɔ yi hyɛ ɔkwan foforɔ a wɔfa so dwene, deɛ ɛde mpaemuka mu nteaseɛ di kan sene anammɔn a ɛho hia, a ɛde kɔ mmara a ɛyɛ den na ɛtumi gyina mfomsoɔ ano.

a wɔde ahyɛ mu "Template metaprogramming titiriw yɛ kasa a ɛyɛ adwuma a wɔde ahyɛ C++ mu. Ɛyɛ adwinnade a tumi wom, nanso ɛhwehwɛ sɛ wosusuw nhyehyɛe ahorow ho wɔ ɔkwan foforo so —ɔkwan a ɛtaa yɛ nea ɛnyɛ adwene na ɛyɛ akontaabu kɛse." — C++ Gyinapɛn Boayikuw no muni

Nneɛma a Wɔde Di Dwuma wɔ Modular System mu

Bere a factorial nhwɛsoɔ no yɛ adesua no, tumi ankasa a ɛwɔ Lisp-style TMP mu no hyerɛn wɔ dwumadie a mfasoɔ wɔ so a ɛnya mfasoɔ firi zero-runtime-overhead abstractions mu. Sɛ nhwɛso no, wobetumi de ayɛ data nhyehyɛe a ɛyɛ papa kɛse a ɛfa ɔkwan pɔtee bi a wɔde ama ho, de agye nhyehyɛe a ɛyɛ den atom wɔ bere a wɔboaboa ano, anaasɛ wɔde nhyehyɛe a ɛyɛ nwonwa te sɛ Policy-Based Design adi dwuma. Wɔ nsɛm a ɛfa platform te sɛ Mewayz a ne botae ne sɛ ɛbɛyɛ modular business OS ho no, saa akwan yi som bo kɛse. Wɔma yɛn kwan ma yɛkyekye nneɛma atitiriw a ɛyɛ nwonwa a ɛyɛ mmerɛw na ɛyɛ adwuma yiye soronko. Wobetumi de TMP ayɛ module bi API de ahyɛ adwumayɛ ho mmara ne data abusuabɔ mu den wɔ type level no so, akyere nhyehyɛe a ɛnteɛ a ebetumi aba bere tenten ansa na wɔde softwea no adi dwuma. Saa ahobanbɔ-bere ahobanbɔ yi ho hia kɛse ma nhyehyɛe a wotumi de ho to so, a wotumi sesa a nnwuma gyina so.

Nkɔsoɔ ne Daakye a ɛwɔ `constexpr`

Ná wɔtaa kasa tia C++ TMP mfiase no wɔ ne cryptic syntax ne brɛoo bere a wɔde boaboa ano no ho. Esiane sɛ wohu eyi nti, C++ gyinapɛn boayikuw no de fi saa bere no de nneɛma a ɛyɛ den ma developer-friendly compile-time features aba, titiriw ne `constexpr` ne, nnansa yi ara, `consteval`. Saa nneɛma yi ma kwan ma wɔde C++ syntax a wonim, a ɛho hia a ɛyɛ adwuma wɔ compile-time mu no kyerɛw akontaabu pii a bere bi na ɛhwehwɛ sɛ wɔyɛ template tricks a ɛyɛ den no. Nanso, Lisp-style TMP kwan no da so ara fata ma type-based computations ne scenarios a ɛhia sɛ wɔdi so titire paa wɔ template instantiation process no so. Nnɛyi C++ developer no seesei wɔ nnwinnadeɛ ahodoɔ, ɛfiri atetesɛm TMP so kɔsi `constexpr` dwumadie so, a ɛma wɔn kwan ma wɔpaw adwinnadeɛ a ɛfata ma adwuma no na wɔkyerɛw metaprograms a ɛho tew, a wɔtumi hwɛ so yie.

Nsɛmmisa a Wɔtaa Bisa

Comiler Magic a ɛsono: Lisp-Style C++ Template Metaprogramming

Wɔ software nkɔsoɔ asase kɛseɛ no mu no, C++ agye din wɔ ne raw power ne adwumayɛ ho. Nanso, wɔde nhwɛsode bi a ɛkame ayɛ sɛ ɛte sɛ nea ɛyɛ ahɔho de asie ne nhyehyɛe a ɛyɛ den a ɛboaboa ano no mu: template metaprogramming (TMP). Sɛ wɔde kɔ ne ntease mu koraa a, C++ TMP fi ase te sɛ nhyehyɛe kasa a ɛyɛ adwuma wɔ n’ankasa mu, nea ɛyɛ adwuma koraa wɔ bere a wɔaboaboa ano. Nsɛdi a ɛne Lisp, nhyehyɛe kasa a akyɛ na ɛwɔ nkɛntɛnso sen biara no mu biako no yɛ nwonwa na emu dɔ. Saa kwan yi ma wɔn a wɔyɛ no tumi yi kɔmputa ne nteaseɛ a ɛyɛ den fi runtime so kɔ compile-time so, na ɛyɛ code a ɛyɛ adwuma yie na ɛyɛ type-safe. Saa Lisp-style kwan yi nteaseɛ yɛ ade titire a ɛbɛma yɛabue abstraction level foforɔ, nnyinasosɛm a yɛbu no sɛ ɛsom boɔ kɛseɛ wɔ Mewayz berɛ a yɛresi adwumayɛ nhyehyɛeɛ a ɛyɛ den, modular.

Akwanhyia Dwumadie Kasa a Ɛwɔ C++

Wɔyɛɛ C++ nsusuiɛ mfitiaseɛ no maa type substitution a ɛnyɛ den, te sɛ `List` anaa `List` a wɔbɛbɔ. Nanso, C++ gyinapɛn no, wɔ ne nyinaa akyi di mu no, ɛde Turing-kasa ketewa a edi mũ bae wɔ akwanhyia mu. Wei kyerɛ sɛ, wɔ nsusuiɛ mu no, akontabuo biara a dwumadie bi bɛtumi ayɛ no nso, C++ compiler no nso bɛtumi ayɛ wɔ template instantiation dwumadie no mu. Saa tumi yi a wohuu no ma wɔwoo template metaprogramming. Wohui sɛ ɛdenam template specialization, recursion, ne template parameters a obi de di dwuma so no, obetumi akyerɛw program ahorow a compiler no yɛ bere a ɔresi wo application no. Saa compile-time "kasa" yi nni nsakrae biara wɔ atetesɛm ntease mu; ne tebea no wɔ template parameters no ankasa mu, na ne control structures no gyina recursion ne conditional compilation so.

Adwene a Ɛyɛ Dwumadi, a ɛte sɛ Lisp a Wogye tom

Sɛ obi bɛkyerɛw template metaprograms yie a, ɛsɛ sɛ ɔfa dwumadie nhyehyɛeɛ adwene, te sɛ Lisp programmer. Tebea anaa loop ahorow biara nni hɔ a ɛsakra wɔ ntease a wɔde di dwuma wɔ tete mmere mu no mu. Mmom no, biribiara nam recursion ne manipulation of types ne compile-time constants so na ɛba. Susuw nhwɛso tiawa bi ho hwɛ: factorial a wobu akontaa. Wɔ Lisp mu no, wobɛtumi de recursive function adi dwuma. Wɔ C++ TMP mu no, ɔkwan no di nsɛ wɔ ɔkwan a ɛyɛ nwonwa so, nanso ɛne ahorow ne botae ahorow yɛ adwuma.

Nneɛma a Wɔde Di Dwuma a Wɔde Di Dwuma wɔ Modular System mu

Bere a factorial nhwɛsoɔ no yɛ adesua no, tumi ankasa a ɛwɔ Lisp-style TMP mu no hyerɛn wɔ dwumadie a mfasoɔ wɔ so a ɛnya mfasoɔ firi zero-runtime-overhead abstractions mu. Sɛ nhwɛso no, wobetumi de ayɛ data nhyehyɛe a ɛyɛ papa kɛse a ɛfa ɔkwan pɔtee bi a wɔde ama ho, de agye nhyehyɛe a ɛyɛ den atom wɔ bere a wɔboaboa ano, anaasɛ wɔde nhyehyɛe a ɛyɛ nwonwa te sɛ Policy-Based Design adi dwuma. Wɔ nsɛm a ɛfa platform te sɛ Mewayz a ne botae ne sɛ ɛbɛyɛ modular business OS ho no, saa akwan yi som bo kɛse. Wɔma yɛn kwan ma yɛkyekye nneɛma atitiriw a ɛyɛ nwonwa a ɛyɛ mmerɛw na ɛyɛ adwuma yiye soronko. Wobetumi de TMP ayɛ module bi API de ahyɛ adwumayɛ ho mmara ne data abusuabɔ mu den wɔ type level no so, akyere nhyehyɛe a ɛnteɛ a ebetumi aba bere tenten ansa na wɔde softwea no adi dwuma. Saa ahobanbɔ-bere ahobanbɔ yi ho hia kɛse ma nhyehyɛe a wotumi de ho to so, a wotumi sesa a nnwuma gyina so.

Nkɔsoɔ ne Daakye a ɛwɔ `constexpr`

Ná wɔtaa kasa tia C++ TMP mfiase no wɔ ne cryptic syntax ne brɛoo bere a wɔde boaboa ano no ho. Esiane sɛ wohu eyi nti, C++ gyinapɛn boayikuw no de fi saa bere no de nneɛma a ɛyɛ den ma developer-friendly compile-time features aba, titiriw ne `constexpr` ne, nnansa yi ara, `consteval`. Saa nneɛma yi ma kwan ma wɔde C++ syntax a wonim, a ɛho hia a ɛyɛ adwuma wɔ compile-time mu no kyerɛw akontaabu pii a bere bi na ɛhwehwɛ sɛ wɔyɛ template tricks a ɛyɛ den no. Nanso, Lisp-style TMP kwan no da so ara fata ma type-based computations ne scenarios a ɛhia sɛ wɔdi so titire paa wɔ template instantiation process no so. Nnɛyi C++ developer no seesei wɔ nnwinnadeɛ ahodoɔ, ɛfiri atetesɛm TMP so kɔsi `constexpr` dwumadie so, a ɛma wɔn kwan ma wɔpaw adwinnadeɛ a ɛfata ma adwuma no na wɔkyerɛw metaprograms a ɛho tew, a wɔtumi hwɛ so yie.