CSE 3302Lecture'10:'Modules'and'separate'compila5on23'Feb'2010Nate'NystromUniversity'of'Texas'at'ArlingtonThursday, February 25, 2010ModulesKey'to'buildi ng'large'soDware'systems'is'ability'to'organize'the'program'into'modules'with'clean,'small'interfacesA'module'iden5fies'an'abstrac5on'in'the'program◾e.g.,%a%logical%component,%an%abstract%data%type2Thursday, February 25, 2010Advantages of modularityaggrega5onencapsula5onindependenceseparate'compila5oncode'reuse3Thursday, February 25, 2010AggregationModules'provide'a'higherJlevel'organiza5on'of'the'programEasier'to'keep'track'of'what'different'parts'of'the'program'are'supposed'to'do4Thursday, February 25, 2010EncapsulationInforma5on'hidingImplementa5on'details'can'be'made'not'visible'to'other'modulesCan'reimplement'module'without'affec5ng'others'5Thursday, February 25, 2010Independenceminimize'dependencies'between'modulesmodule'interface'should'specify'dependenciesmakes'it'possible'to'develop'on e'part'of'th e'program'independently'of'other'parts6Thursday, February 25, 2010Separate compilationCan'compile'a'mod ule'separately'from'othersIf'one'module'changes,'only'that'module'needs'to'be'recompiledEach'module'can'be'compiled'independently,'checking'against'the'interfaces'of'the'other'modules.During'linking,'resolve'references'from'one'module'to'another,'construc5ng'a'complete'program.7Thursday, February 25, 2010Code reuseCan'reuse'modules'in'other'programs'if'they'provide'other'generalJpurpose'func5onalityExamples:◾libraries◾frameworks8Thursday, February 25, 2010ModulesSeparate'specifica-on/and/implementa-on◾specifica5on◾describes%what%a%piece%of%code%is%supposed%to%do◾provided%by%interfaces◾implementa5on◾describes%how%to%do%it◾provided%by%modules9Thursday, February 25, 2010InterfacesNo,'not'Java'interfaces!◾more'on'that'laterAn'interface'is:◾Collec5on'of'types◾Data'declara5ons◾Pro cedure'signatures10Thursday, February 25, 2010ModulesImplementa5ons'for'proceduresAddi5onal'data'and'procedures◾not'present'in'the'interface◾private'and'not'available'to'other'moduelesIni5aliza5on'code11Thursday, February 25, 2010Language supportMany'languages'provide'modules'or'moduleJlike'structuresBut'they'use'different'names:◾Pascal'–'units◾Ada'–'packages◾Java'–"packages,"classes◾ML'–'structs'(but'usually'just'called'modules)◾ModulaJ3'–'modules12Thursday, February 25, 2010Modula-3We’ll'explore'the'essence'of'modu les'usi ng'Mod ul aJ3Why'M3?◾Not'clu^ered'with'other'features'(viz.'objects)◾Not'completely'ad'hoc'(C)13Thursday, February 25, 2010Separating spec and implementationTwo'constructs:◾Interfaces◾Modules14Thursday, February 25, 2010Modula-3 interfacesInterface'for'a'Util'module'that'provides'u5lity'func5ons'for'arrays'of'integersINTERFACE-Util;TYPE-A-=-ARRAY-OF-INTEGER;PROCEDURE-Sort(a:-A);PROCEDURE-Max(a:-A):-INTEGER;END-Util.15Provides'signatures'for'two'procedures'opera5ng'on'type'A.Defines'a'type'AThursday, February 25, 2010Modula-3 modulesImplementa5on'of'the'Util'module:MODULE-Util-EXPORTS-Util;PROCEDURE-Sort(a:-A)-=---BEGIN-(*-code-for-Sort-*)-END-Sort;PROCEDURE-Max(a:-A):-INTEGER-=---BEGIN-(*-code-for-Max-*)-END-Max;PROCEDURE-Compare(a:-A,-b:-A):-INTEGER-=---BEGIN-(*-code-for-Compare-*)-END-Compare;END-Util.16EXPORTS'indicates'what'interface'this'module'implements.'Thursday, February 25, 2010Modula-3 modulesImplementa5on'of'the'Util'module:MODULE-Util-EXPORTS-Util;PROCEDURE-Sort(a:-A)-=---BEGIN-(*-code-for-Sort-*)-END-Sort;PROCEDURE-Max(a:-A):-INTEGER-=---BEGIN-(*-code-for-Max-*)-END-Max;PROCEDURE-Compare(a:-A,-b:-A):-INTEGER-=---BEGIN-(*-code-for-Compare-*)-END-Compare;END-Util.17Module'can'define'more'members'than'tho se'in'i nterface.''Not'visible'to'other'modules.Thursday, February 25, 2010FeaturesModules'and'interfaces◾specify'a'namespace'collec5ng'related'types,'declara5ons,'and'proceduresInterface◾specifies'names'that'are'exported'(i.e.,'visibl e'to)'other'modulesModule◾defines'the'implementa5on'of'a'given'interface◾implementa5on'may'include'members'not'exported18Thursday, February 25, 2010CC'supports'ad/hoc/modulesLarge'programs'are'modularized'by'breaking'the'program'into'mul5ple'.c'filesEach'.c'file'is'compiled'into'a'object'(.o)'fileMul5ple'.o'files'are'linked'together'into'an'executable'or'libraryUse'header'(.h)'files'to'share'declara5ons19Thursday, February 25, 2010Separate compilation in CCan'compile'each'.c'fi le'separatelyCan'refer'to'code'in'other'.c'files'using'extern◾extern-int-strcmp(const-char-*,-const-char-*);◾extern-float-BIG_ARRAY[N];20Thursday, February 25, 2010Separating spec and implementationBy/conven-on,'separate'specifica5on'and'implementa5on'by'using'header'(.h)'filesPut'specifica5on'for'a'module'in'.h'file◾type'declara5ons'(typedefs,'structs)◾variable'declara5ons◾func5on'declara5ons'(prototypes)Put'implementa5on'in'.c'fileBut'not'quite:◾some'implementa5on'in'.h'file◾inline'func5ons,'macros,'C++'templates21Thursday, February 25, 2010Information hidingBy'default,'any'declara5on'in'file'1'can'be'made'visible'in'file'2'by'declaring'a'prototype'in'file'2One'mechanism'for'informa5on'hi di ng'in 'C:'static◾static'variables'and'func5ons'in'one'file'are'not'visible'in'other'files22Thursday, February 25, 2010Modules in JavaSeparate'specifica5on'and'implementa5on'with:◾Specifica5on'given'by'interfaces◾Implementa5on'given'in'classesBut,'separa5on'not'enforced◾not'required'to'use'interfaces◾can'use'other'classes'directly23Thursday, February 25, 2010Java interfacesinterface-IntRef-{----void-set(int-x);----int-get();}Specifies'a'set'of'public'methods'all'classes'implemen5ng'the'interface'must'provide.class-C-implements-IntRef-{----private-int-v;----public-void-set(int-x)-{-v-=-x;-}-----public-int-get()-{-return-v;-}}24Thursday, February 25, 2010PackagesA'package'is'a'collec5on'of'related'classes'and'interfaces.Namespaces'provided'by'packages◾but,'packages'don’t'separate'specifica5on'and'implementa5on◾no'way'to'say'several 'mutual ly /dependent'classes'implement'several'mutually'dependent'interfaces'◾can'declare'classes,'interface,'methods,'fields'to'be'packageJscoped'––'visibl e'onl y'to'other'members'of'the'package.25Thursday, February 25, 2010Using a module26Thursday, February 25, 2010Modula-3
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