外文翻譯-委托

畢業(yè)設(shè)計(jì)（論文）外文文獻(xiàn)原文及譯文學(xué)院計(jì)算機(jī)科學(xué)與工程學(xué)院專業(yè)網(wǎng)絡(luò)工程原文DELEGATEDELEGATESENABLESCENARIOSTHATOTHERLANGUAGESSUCHASC,PASCAL,ANDMODULAHAVEADDRESSEDWITHFUNCTIONPOINTERSUNLIKECFUNCTIONPOINTERS,HOWEVER,DELEGATESAREFULLYOBJECTORIENTED,ANDUNLIKECPOINTERSTOMEMBERFUNCTIONS,DELEGATESENCAPSULATEBOTHANOBJECTINSTANCEANDAMETHODADELEGATEDECLARATIONDEFINESACLASSTHATISDERIVEDFROMTHECLASSSYSTEMDELEGATEADELEGATEINSTANCEENCAPSULATESANINVOCATIONLIST,WHICHISALISTOFONEORMOREMETHODS,EACHOFWHICHISREFERREDTOASACALLABLEENTITYFORINSTANCEMETHODS,ACALLABLEENTITYCONSISTSOFANINSTANCEANDAMETHODONTHATINSTANCEFORSTATICMETHODS,ACALLABLEENTITYCONSISTSOFJUSTAMETHODINVOKINGADELEGATEINSTANCEWITHANAPPROPRIATESETOFARGUMENTSCAUSESEACHOFTHEDELEGATESCALLABLEENTITIESTOBEINVOKEDWITHTHEGIVENSETOFARGUMENTSANINTERESTINGANDUSEFULPROPERTYOFADELEGATEINSTANCEISTHATITDOESNOTKNOWORCAREABOUTTHECLASSESOFTHEMETHODSITENCAPSULATESALLTHATMATTERSISTHATTHOSEMETHODSBECOMPATIBLEWITHTHEDELEGATESTYPETHISMAKESDELEGATESPERFECTLYSUITEDFOR“ANONYMOUS”INVOCATION11DELEGATEDECLARATIONSADELEGATEDECLARATIONISATYPEDECLARATIONTHATDECLARESANEWDELEGATETYPEDELEGATEDECLARATIONATTRIBUTESOPTDELEGATEMODIFIERSOPTDELEGATERETURNTYPEIDENTIFIERVARIANTTYPEPARAMETERLISTOPTFORMALPARAMETERLISTOPTTYPEPARAMETERCONSTRAINTSCLAUSESOPTDELEGATEMODIFIERSDELEGATEMODIFIERDELEGATEMODIFIERSDELEGATEMODIFIERDELEGATEMODIFIERNEWPUBLICPROTECTEDINTERNALPRIVATEITISACOMPILETIMEERRORFORTHESAMEMODIFIERTOAPPEARMULTIPLETIMESINADELEGATEDECLARATIONTHENEWMODIFIERISONLYPERMITTEDONDELEGATESDECLAREDWITHINANOTHERTYPE,INWHICHCASEITSPECIFIESTHATSUCHADELEGATEHIDESANINHERITEDMEMBERBYTHESAMENAMETHEPUBLIC,PROTECTED,INTERNAL,ANDPRIVATEMODIFIERSCONTROLTHEACCESSIBILITYOFTHEDELEGATETYPEDEPENDINGONTHECONTEXTINWHICHTHEDELEGATEDECLARATIONOCCURS,SOMEOFTHESEMODIFIERSMAYNOTBEPERMITTEDTHEDELEGATESTYPENAMEISIDENTIFIERTHEOPTIONALFORMALPARAMETERLISTSPECIFIESTHEPARAMETERSOFTHEDELEGATE,ANDRETURNTYPEINDICATESTHERETURNTYPEOFTHEDELEGATETHEOPTIONALVARIANTTYPEPARAMETERLISTSPECIFIESTHETYPEPARAMETERSTOTHEDELEGATEITSELFTHERETURNTYPEOFADELEGATETYPEMUSTBEEITHERVOID,OROUTPUTSAFEALLTHEFORMALPARAMETERTYPESOFADELEGATETYPEMUSTBEINPUTSAFEADDITIONALLY,ANYOUTORREFPARAMETERTYPESMUSTALSOBEOUTPUTSAFENOTETHATEVENOUTPARAMETERSAREREQUIREDTOBEINPUTSAFE,DUETOALIMITIATIONOFTHEUNDERLYINGEXECUTIONPLATFORMDELEGATETYPESINCARENAMEEQUIVALENT,NOTSTRUCTURALLYEQUIVALENTSPECIFICALLY,TWODIFFERENTDELEGATETYPESTHATHAVETHESAMEPARAMETERLISTSANDRETURNTYPEARECONSIDEREDDIFFERENTDELEGATETYPESHOWEVER,INSTANCESOFTWODISTINCTBUTSTRUCTURALLYEQUIVALENTDELEGATETYPESMAYCOMPAREASEQUALFOREXAMPLEDELEGATEINTD1INTI,DOUBLEDCLASSAPUBLICSTATICINTM1INTA,DOUBLEBCLASSBDELEGATEINTD2INTC,DOUBLEDPUBLICSTATICINTM1INTF,DOUBLEGPUBLICSTATICVOIDM2INTK,DOUBLELPUBLICSTATICINTM3INTGPUBLICSTATICVOIDM4INTGTHEDELEGATETYPESD1ANDD2AREBOTHCOMPATIBLEWITHTHEMETHODSAM1ANDBM1,SINCETHEYHAVETHESAMERETURNTYPEANDPARAMETERLISTHOWEVER,THESEDELEGATETYPESARETWODIFFERENTTYPES,SOTHEYARENOTINTERCHANGEABLETHEDELEGATETYPESD1ANDD2AREINCOMPATIBLEWITHTHEMETHODSBM2,BM3,ANDBM4,SINCETHEYHAVEDIFFERENTRETURNTYPESORPARAMETERLISTSLIKEOTHERGENERICTYPEDECLARATIONS,TYPEARGUMENTSMUSTBEGIVENTOCREATEACONSTRUCTEDDELEGATETYPETHEPARAMETERTYPESANDRETURNTYPEOFACONSTRUCTEDDELEGATETYPEARECREATEDBYSUBSTITUTING,FOREACHTYPEPARAMETERINTHEDELEGATEDECLARATION,THECORRESPONDINGTYPEARGUMENTOFTHECONSTRUCTEDDELEGATETYPETHERESULTINGRETURNTYPEANDPARAMETERTYPESAREUSEDINDETERMININGWHATMETHODSARECOMPATIBLEWITHACONSTRUCTEDDELEGATETYPEFOREXAMPLEDELEGATEBOOLPREDICATETVALUECLASSXSTATICBOOLFINTISTATICBOOLGSTRINGSTHEDELEGATETYPEPREDICATEISCOMPATIBLEWITHTHEMETHODXFANDTHEDELEGATETYPEPREDICATEISCOMPATIBLEWITHTHEMETHODXGTHEONLYWAYTODECLAREADELEGATETYPEISVIAADELEGATEDECLARATIONADELEGATETYPEISACLASSTYPETHATISDERIVEDFROMSYSTEMDELEGATEDELEGATETYPESAREIMPLICITLYSEALED,SOITISNOTPERMISSIBLETODERIVEANYTYPEFROMADELEGATETYPEITISALSONOTPERMISSIBLETODERIVEANONDELEGATECLASSTYPEFROMSYSTEMDELEGATENOTETHATSYSTEMDELEGATEISNOTITSELFADELEGATETYPEITISACLASSTYPEFROMWHICHALLDELEGATETYPESAREDERIVEDCPROVIDESSPECIALSYNTAXFORDELEGATEINSTANTIATIONANDINVOCATIONEXCEPTFORINSTANTIATION,ANYOPERATIONTHATCANBEAPPLIEDTOACLASSORCLASSINSTANCECANALSOBEAPPLIEDTOADELEGATECLASSORINSTANCE,RESPECTIVELYINPARTICULAR,ITISPOSSIBLETOACCESSMEMBERSOFTHESYSTEMDELEGATETYPEVIATHEUSUALMEMBERACCESSSYNTAXTHESETOFMETHODSENCAPSULATEDBYADELEGATEINSTANCEISCALLEDANINVOCATIONLISTWHENADELEGATEINSTANCEISCREATEDFROMASINGLEMETHOD,ITENCAPSULATESTHATMETHOD,ANDITSINVOCATIONLISTCONTAINSONLYONEENTRYHOWEVER,WHENTWONONNULLDELEGATEINSTANCESARECOMBINED,THEIRINVOCATIONLISTSARECONCATENATEDINTHEORDERLEFTOPERANDTHENRIGHTOPERANDTOFORMANEWINVOCATIONLIST,WHICHCONTAINSTWOORMOREENTRIESDELEGATESARECOMBINEDUSINGTHEBINARYANDOPERATORSADELEGATECANBEREMOVEDFROMACOMBINATIONOFDELEGATES,USINGTHEBINARYANDOPERATORSDELEGATESCANBECOMPAREDFOREQUALITYTHEFOLLOWINGEXAMPLESHOWSTHEINSTANTIATIONOFANUMBEROFDELEGATES,ANDTHEIRCORRESPONDINGINVOCATIONLISTSDELEGATEVOIDDINTXCLASSCPUBLICSTATICVOIDM1INTIPUBLICSTATICVOIDM2INTICLASSTESTSTATICVOIDMAINDCD1NEWDCM1/M1DCD2NEWDCM2/M2DCD3CD1CD2/M1M2DCD4CD3CD1/M1M2M1DCD5CD4CD3/M1M2M1M1M2WHENCD1ANDCD2AREINSTANTIATED,THEYEACHENCAPSULATEONEMETHODWHENCD3ISINSTANTIATED,ITHASANINVOCATIONLISTOFTWOMETHODS,M1ANDM2,INTHATORDERCD4SINVOCATIONLISTCONTAINSM1,M2,ANDM1,INTHATORDERFINALLY,CD5SINVOCATIONLISTCONTAINSM1,M2,M1,M1,ANDM2,INTHATORDERFORMOREEXAMPLESOFCOMBININGASWELLASREMOVINGDELEGATES12DELEGATECOMPATIBILITYAMETHODORDELEGATEMISCOMPATIBLEWITHADELEGATETYPEDIFALLOFTHEFOLLOWINGARETRUEDANDMHAVETHESAMENUMBEROFPARAMETERS,ANDEACHPARAMETERINDHASTHESAMEREFOROUTMODIFIERSASTHECORRESPONDINGPARAMETERINMFOREACHVALUEPARAMETERAPARAMETERWITHNOREFOROUTMODIFIER,ANIDENTITYCONVERSIONORIMPLICITREFERENCECONVERSIONEXISTSFROMTHEPARAMETERTYPEINDTOTHECORRESPONDINGPARAMETERTYPEINMFOREACHREFOROUTPARAMETER,THEPARAMETERTYPEINDISTHESAMEASTHEPARAMETERTYPEINMANIDENTITYORIMPLICITREFERENCECONVERSIONEXISTSFROMTHERETURNTYPEOFMTOTHERETURNTYPEOFD13DELEGATEINSTANTIATIONANINSTANCEOFADELEGATEISCREATEDBYADELEGATECREATIONEXPRESSIONORACONVERSIONTOADELEGATETYPETHENEWLYCREATEDDELEGATEINSTANCETHENREFERSTOEITHERTHESTATICMETHODREFERENCEDINTHEDELEGATECREATIONEXPRESSION,ORTHETARGETOBJECTWHICHCANNOTBENULLANDINSTANCEMETHODREFERENCEDINTHEDELEGATECREATIONEXPRESSION,ORANOTHERDELEGATEFOREXAMPLEDELEGATEVOIDDINTXCLASSCPUBLICSTATICVOIDM1INTIPUBLICVOIDM2INTICLASSTESTSTATICVOIDMAINDCD1NEWDCM1/STATICMETHODCTNEWCDCD2NEWDTM2/INSTANCEMETHODDCD3NEWDCD2/ANOTHERDELEGATEONCEINSTANTIATED,DELEGATEINSTANCESALWAYSREFERTOTHESAMETARGETOBJECTANDMETHODREMEMBER,WHENTWODELEGATESARECOMBINED,ORONEISREMOVEDFROMANOTHER,ANEWDELEGATERESULTSWITHITSOWNINVOCATIONLISTTHEINVOCATIONLISTSOFTHEDELEGATESCOMBINEDORREMOVEDREMAINUNCHANGED14DELEGATEINVOCATIONCPROVIDESSPECIALSYNTAXFORINVOKINGADELEGATEWHENANONNULLDELEGATEINSTANCEWHOSEINVOCATIONLISTCONTAINSONEENTRYISINVOKED,ITINVOKESTHEONEMETHODWITHTHESAMEARGUMENTSITWASGIVEN,ANDRETURNSTHESAMEVALUEASTHEREFERREDTOMETHODIFANEXCEPTIONOCCURSDURINGTHEINVOCATIONOFSUCHADELEGATE,ANDTHATEXCEPTIONISNOTCAUGHTWITHINTHEMETHODTHATWASINVOKED,THESEARCHFORANEXCEPTIONCATCHCLAUSECONTINUESINTHEMETHODTHATCALLEDTHEDELEGATE,ASIFTHATMETHODHADDIRECTLYCALLEDTHEMETHODTOWHICHTHATDELEGATEREFERREDINVOCATIONOFADELEGATEINSTANCEWHOSEINVOCATIONLISTCONTAINSMULTIPLEENTRIESPROCEEDSBYINVOKINGEACHOFTHEMETHODSINTHEINVOCATIONLIST,SYNCHRONOUSLY,INORDEREACHMETHODSOCALLEDISPASSEDTHESAMESETOFARGUMENTSASWASGIVENTOTHEDELEGATEINSTANCEIFSUCHADELEGATEINVOCATIONINCLUDESREFERENCEPARAMETERS,EACHMETHODINVOCATIONWILLOCCURWITHAREFERENCETOTHESAMEVARIABLECHANGESTOTHATVARIABLEBYONEMETHODINTHEINVOCATIONLISTWILLBEVISIBLETOMETHODSFURTHERDOWNTHEINVOCATIONLISTIFTHEDELEGATEINVOCATIONINCLUDESOUTPUTPARAMETERSORARETURNVALUE,THEIRFINALVALUEWILLCOMEFROMTHEINVOCATIONOFTHELASTDELEGATEINTHELISTIFANEXCEPTIONOCCURSDURINGPROCESSINGOFTHEINVOCATIONOFSUCHADELEGATE,ANDTHATEXCEPTIONISNOTCAUGHTWITHINTHEMETHODTHATWASINVOKED,THESEARCHFORANEXCEPTIONCATCHCLAUSECONTINUESINTHEMETHODTHATCALLEDTHEDELEGATE,ANDANYMETHODSFURTHERDOWNTHEINVOCATIONLISTARENOTINVOKEDATTEMPTINGTOINVOKEADELEGATEINSTANCEWHOSEVALUEISNULLRESULTSINANEXCEPTIONOFTYPESYSTEMNULLREFERENCEEXCEPTIONTHEFOLLOWINGEXAMPLESHOWSHOWTOINSTANTIATE,COMBINE,REMOVE,ANDINVOKEDELEGATESUSINGSYSTEMDELEGATEVOIDDINTXCLASSCPUBLICSTATICVOIDM1INTICONSOLEWRITELINE“CM1“IPUBLICSTATICVOIDM2INTICONSOLEWRITELINE“CM2“IPUBLICVOIDM3INTICONSOLEWRITELINE“CM3“ICLASSTESTSTATICVOIDMAINDCD1NEWDCM1CD11/CALLM1DCD2NEWDCM2CD22/CALLM2DCD3CD1CD2CD310/CALLM1THENM2CD3CD1CD320/CALLM1,M2,THENM1CCNEWCDCD4NEWDCM3CD3CD4CD330/CALLM1,M2,M1,THENM3CD3CD1/REMOVELASTM1CD340/CALLM1,M2,THENM3CD3CD4CD350/CALLM1THENM2CD3CD2CD360/CALLM1CD3CD2/IMPOSSIBLEREMOVALISBENIGNCD360/CALLM1CD3CD1/INVOCATIONLISTISEMPTYSOCD3ISNULL/CD370/SYSTEMNULLREFERENCEEXCEPTIONTHROWNCD3CD1/IMPOSSIBLEREMOVALISBENIGNASSHOWNINTHESTATEMENTCD3CD1,ADELEGATECANBEPRESENTINANINVOCATIONLISTMULTIPLETIMESINTHISCASE,ITISSIMPLYINVOKEDONCEPEROCCURRENCEINANINVOCATIONLISTSUCHASTHIS,WHENTHATDELEGATEISREMOVED,THELASTOCCURRENCEINTHEINVOCATIONLISTISTHEONEACTUALLYREMOVEDIMMEDIATELYPRIORTOTHEEXECUTIONOFTHEFINALSTATEMENT,CD3CD1,THEDELEGATECD3REFERSTOANEMPTYINVOCATIONLISTATTEMPTINGTOREMOVEADELEGATEFROMANEMPTYLISTORTOREMOVEANONEXISTENTDELEGATEFROMANONEMPTYLISTISNOTANERRORTHEOUTPUTPRODUCEDISCM11CM22CM110CM210CM120CM220CM120CM130CM230CM130CM330CM140CM240CM340CM150CM250CM160CM160譯文委托委托是用來(lái)處理其他語(yǔ)言（如C、PASCAL和MODULA）需用函數(shù)指針來(lái)處理的情況的。不過(guò)與C函數(shù)指針不同，委托是完全面向?qū)ο蟮?；另外，C指針僅指向成員函數(shù)，而委托同時(shí)封裝了對(duì)象實(shí)例和方法。委托聲明定義一個(gè)從SYSTEMDELEGATE類派生的類。委托實(shí)例封裝了一個(gè)調(diào)用列表，該列表列出了一個(gè)或多個(gè)方法，每個(gè)方法稱為一個(gè)可調(diào)用實(shí)體。對(duì)于實(shí)例方法，可調(diào)用實(shí)體由該方法和一個(gè)相關(guān)聯(lián)的實(shí)例組成。對(duì)于靜態(tài)方法，可調(diào)用實(shí)體僅由一個(gè)方法組成。用一個(gè)適當(dāng)?shù)膮?shù)集來(lái)調(diào)用一個(gè)委托實(shí)例，就是用此給定的參數(shù)集來(lái)調(diào)用該委托實(shí)例的每個(gè)可調(diào)用實(shí)體。委托實(shí)例的一個(gè)有趣且有用的屬性是它不知道也不關(guān)心它所封裝的方法所屬的類；它所關(guān)心的僅限于這些方法必須與委托的類型兼容。這使委托非常適合于“匿名”調(diào)用。委托聲明DELEGATEDECLARATION是一種TYPEDECLARATION，它聲明一個(gè)新的委托類型。DELEGATEDECLARATIONATTRIBUTESOPTDELEGATEMODIFIERSOPTDELEGATERETURNTYPEIDENTIFIERVARIANTTYPEPARAMETERLISTOPTFORMALPARAMETERLISTOPTTYPEPARAMETERCONSTRAINTSCLAUSESOPTDELEGATEMODIFIERSDELEGATEMODIFIERDELEGATEMODIFIERSDELEGATEMODIFIERDELEGATEMODIFIERNEWPUBLICPROTECTEDINTERNALPRIVATE同一修飾符在一個(gè)委托聲明中多次出現(xiàn)屬于編譯時(shí)錯(cuò)誤。NEW修飾符僅允許在其他類型中聲明的委托上使用，在這種情況下該修飾符表示所聲明的委托會(huì)隱藏具有相同名稱的繼承成員。PUBLIC、PROTECTED、INTERNAL和PRIVATE修飾符控制委托類型的可訪問(wèn)性。根據(jù)委托聲明所在的上下文，可能不允許使用其中某些修飾符。上述的語(yǔ)法產(chǎn)生式中，IDENTIFIER用于指定委托的類型名稱?？蛇x的FORMALPARAMETERLIST用于指定委托的參數(shù)，而RETURNTYPE則指定委托的返回類型。可選的VARIANTTYPEPARAMETERLIST指定委托本身的類型形參。委托類型的返回類型必須為VOID或輸出安全。委托類型的所有形參類型都必須是輸入安全的。此外，所有OUT或REF形參類型也必須是輸出安全的。請(qǐng)注意，由于基礎(chǔ)執(zhí)行平臺(tái)的限制，甚至OUT形參也必須是輸入安全的。C中的委托類型是名稱等效的，而不是結(jié)構(gòu)等效的。具體地說(shuō)，對(duì)于兩個(gè)委托類型，即使它們具有相同的參數(shù)列表和返回類型，仍被認(rèn)為是不同的兩個(gè)委托類型。但是，兩個(gè)不同但結(jié)構(gòu)上等效的委托類型的實(shí)例可能比較為相等。例如DELEGATEINTD1INTI,DOUBLEDCLASSAPUBLICSTATICINTM1INTA,DOUBLEBCLASSBDELEGATEINTD2INTC,DOUBLEDPUBLICSTATICINTM1INTF,DOUBLEGPUBLICSTATICVOIDM2INTK,DOUBLELPUBLICSTATICINTM3INTGPUBLICSTATICVOIDM4INTG委托類型D1和D2都與方法AM1和BM1兼容，這是因?yàn)樗鼈兙哂邢嗤姆祷仡愋秃蛥?shù)列表；但是，這些委托類型是兩個(gè)不同的類型，所以它們是不可互換的。委托類型D1和D2與方法BM2、BM3和BM4不兼容，這是因?yàn)樗鼈兙哂胁煌姆祷仡愋突騾?shù)列表。與其他泛型類型聲明一樣，必須提供類型實(shí)參才能創(chuàng)建構(gòu)造委托類型。構(gòu)造委托類型的形參類型和返回類型是通過(guò)將委托聲明中的每個(gè)類型形參替換為構(gòu)造委托類型的對(duì)應(yīng)類型實(shí)參來(lái)創(chuàng)建的。結(jié)果返回類型和形參類型用于確定哪些方法與構(gòu)造委托類型兼容。例如DELEGATEBOOLPREDICATETVALUECLASSXSTATICBOOLFINTISTATICBOOLGSTRINGS委托類型PREDICATE與方法XF兼容，委托類型PREDICATE與方法XG兼容。聲明一個(gè)委托類型的唯一方法是通過(guò)DELEGATEDECLARATION。委托類型是從SYSTEMDELEGATE派生的類類型。委托類型隱含為SEALED，所以不允許從一個(gè)委托類型派生任何類型。也不允許從SYSTEMDELEGATE派生非委托類類型。請(qǐng)注意SYSTEMDELEGATE本身不是委托類型；它是從中派生所有委托類型的類類型。C提供了專門的語(yǔ)法用于委托類型的實(shí)例化和調(diào)用。除實(shí)例化外，所有可以應(yīng)用于類或類實(shí)例的操作也可以相應(yīng)地應(yīng)用于委托類或委托實(shí)例。具體而言，可以通過(guò)通常的成員訪問(wèn)語(yǔ)法訪問(wèn)SYSTEMDELEGATE類型的成員。委托實(shí)例所封裝的方法集合稱為調(diào)用列表。從某個(gè)方法創(chuàng)建一個(gè)委托實(shí)例時(shí)，該委托實(shí)例將封裝此方法，此時(shí)，它的調(diào)用列表只包含一個(gè)“入口點(diǎn)”。但是，當(dāng)組合兩個(gè)非空委托實(shí)例時(shí)，它們的調(diào)用列表將連接在一起（按照左操作數(shù)在前、右操作數(shù)在后的順序）以組成一個(gè)新的調(diào)用列表，其中包含兩個(gè)或更多個(gè)“入口點(diǎn)”。委托是使用二元和運(yùn)算符進(jìn)行組合的?？梢允褂枚瓦\(yùn)算符將一個(gè)委托從委托組合中移除。委托間還可以進(jìn)行比較以確定它們是否相等。下面的示例演示多個(gè)委托的實(shí)例化及其相應(yīng)的調(diào)用列表DELEGATEVOIDDINTXCLASSCPUBLICSTATICVOIDM1INTIPUBLICSTATICVOIDM2INTICLASSTESTSTATICVOIDMAINDCD1NEWDCM1/M1DCD2NEWDCM2/M2DCD3CD1CD2/M1M2DCD4CD3CD1/M1M2M1DCD5CD4CD3/M1M2M1M1M2實(shí)例化CD1和CD2時(shí)，它們分別封裝一個(gè)方法。實(shí)例化CD3時(shí)，它的調(diào)用列表有兩個(gè)方法M1和M2，而且順序與此相同。CD4的調(diào)用列表中依次包含M1、M2和M1。最后，CD5的調(diào)用列表中依次包含M1、M2、M1、M1和M2。有關(guān)組合以及移除委托的更多示例。11委托兼容性如果以下所有條件都成立，則方法或委托M與委托類型D兼容COMPATIBLED和M具有相同數(shù)量的形參，并且D中的每個(gè)形參都具有與M中對(duì)應(yīng)形參相同的REF或OUT修飾符。對(duì)于每個(gè)值形參（沒(méi)有REF或OUT修飾符的形參），存在從D中形參類型到M中對(duì)應(yīng)形參類型的標(biāo)識(shí)轉(zhuǎn)換或隱式引用轉(zhuǎn)換。對(duì)于每個(gè)REF或OUT參數(shù)，D中的參數(shù)類型與M中的參數(shù)類型相同。存在從M的返回類型到D的返回類型的標(biāo)識(shí)或隱式引用轉(zhuǎn)換。12委托實(shí)例化委托的實(shí)例通過(guò)DELEGATECREATIONEXPRESSION或到委托類型的轉(zhuǎn)換進(jìn)行創(chuàng)建。因此，新創(chuàng)建的委托實(shí)例將引用以下各項(xiàng)之一DELEGATECREATIONEXPRESSION中引用的靜態(tài)方法，或者DELEGATECREATIONEXPRESSION中引用的目標(biāo)對(duì)象（此對(duì)象不能為NULL）和實(shí)例方法，或者另一個(gè)委托。例如DELEGATEVOIDDINTXCLASSCPUBLICSTATICVOIDM1INTIPUBLICVOIDM2INTICLASSTESTSTATICVOIDMAINDCD1NEWDCM1/STATICMETHODCTNEWCDCD2NEWDTM2/INSTANCEMETHODDCD3NEWDCD2/ANOTHERDELEGATE委托實(shí)例一旦被實(shí)例化，它將始終引用同一目標(biāo)對(duì)象和方法。記住，當(dāng)組合兩個(gè)委托或者從一個(gè)委托移除另一個(gè)時(shí)，將產(chǎn)生一個(gè)新的委托，該委托具有它自己的調(diào)用列表；被組合或移除的委托的調(diào)用列表將保持不變。13委托調(diào)用C為調(diào)用委托提供了專門的語(yǔ)法。當(dāng)調(diào)用非空的、調(diào)用列表僅包含一個(gè)入