内容讲义案例transform iterator

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TransformI tor

Author: DavidAbrahams,JeremySiek,ThomasWitt

Contact: dave@bo ,

jsiek@,

witt@ive.uni-hannover.de

Organization: BoostConsulting, naUniversityOpenSystemsLab,UniversityofHanoverInstituteforTransportRailwayOperationandConstruction

Date: 2004-11-01

Copyright: CopyrightDavidAbrahams,JeremySiek,andThomasWitt2003.

:Thetransformi toradaptsani torbymodifyingtheoperator*toapplyafunctionobjecttotheresultofdereferencingthei torandreturningtheresult.

TableofContents

transform_i torsynopsistransform_i torrequirementstransform_i tormodelstransform_i toroperationsExample

transform_i torsynopsis

temte<classUnaryFunction,

classI tor,

classReference=use_default,classValue=use_default>

classtransform_i tor

{

public:

typedef/*seebelow*/value_type;typedef/*seebelow*/reference;typedef/*seebelow*/pointer;

typedefi tor_traits<I tor>::difference_typedifference_type;typedef/*seebelow*/i tor_category;

transform_i tor();

transform_i tor(I torconst&x,UnaryFunctionf);

temte<classF2,classI2,classR2,classV2>transform_i tor(

transform_i tor<F2,I2,R2,V2>const&t

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,typenameenable_if_convertible<I2,I tor>::type*=0 //ex-positiononly

,typenameenable_if_convertible<F2,UnaryFunction>::type*=0//ex-positiononly

);

UnaryFunctionfunctor()const;I torconst&base()const;referenceoperator*()const;

transform_i tor&operator++();transform_i tor&operator--();

private:

I torm_i tor;//expositiononlyUnaryFunctionm_f; //expositiononly

};

IfReferenceisuse_defaultthenthereferencememberoftransform_i torisresult_of<UnaryFunction(iteOtherwise,referenceisReference.

IfValueisuse_defaultthenthevalue_typememberisremove_cv<remove_reference<reference>

>::type.Otherwise,value_typeisValue.

IfItormodelsReadableLvalueItorandifItormodelsRandomAccessTraver-salItor,thenitor_categoryisconvertibletorandom_access_itor_tag.Otherwise,ifItormodelsBidirectionalTraversalItor,thenitor_categoryisconvertibletobidi-rectional_itor_tag.Otherwiseitor_categoryisconvertibletoforward_itor_tag.IfItordoesnotmodelReadableLvalueItorthenitor_categoryisconvertibletoin-put_itor_tag.

transform_itorrequirements

ThetypeUnaryFunctionmustbeAssignable,CopyConstructible,andtheexpressionf(*i)mustbevalidwherefisanobjectoftypeUnaryFunction,iisanobjectoftypeItor,andwherethetypeoff(*i)mustberesult_of<UnaryFunction(itor_traits<Itor>::reference)>::type.

TheargumentItorshallmodelReadableItor.

transform_itormodels

Theresultingtransform_itormodelsthemostrefinedofthefollowingthatisalsomodeledby

I tor.

WritableLvalueI toriftransform_i tor::referenceisanon-constreference.

ReadableLvalueI toriftransform_i tor::referenceisaconstreference.

ReadableI torotherwise.

Thetransform_itormodelsthemostrefinedstandardtraversalconceptthatismodeledbytheItorargument.

Iftransform_itorisamodelofReadableLvalueItorthenitmodelsthefollowingoriginalitorconceptsdependingonwhattheItorargumentmodels.

IfI tormodels thentransform_i tormodels

SinglePassI tor InputI tor

ForwardTraversalI tor ForwardI tor

BidirectionalTraversalI tor BidirectionalI torRandomAccessTraversalI tor RandomAccessI tor

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Iftransform_i tormodelsWritableLvalueI torthenitisamutablei tor(asdefinedintheoldi torrequirements).

transform_i tor<F1,X,R1,V1>isinteroperablewithtransform_i tor<F2,Y,R2,V2>

ifandonlyifXisinteroperablewithY.

transform_i toroperations

Inadditiontotheoperationsrequiredbytheconceptsmodeledbytransform_i tor,trans-form_i torprovidesthefollowingoperations.

transform_i tor();

Returns:Aninstanceoftransform_i torwithm_fandm_i tordefaultcon-structed.

transform_i tor(I torconst&x,UnaryFunctionf);

Returns:Aninstanceoftransform_i torwithm_finitializedtofandm_i tor

initializedtox.

temte<classF2,classI2,classR2,classV2>transform_i tor(

transform_i tor<F2,I2,R2,V2>const&t

,typenameenable_if_convertible<I2,I tor>::type*=0 //expo-sitiononly

,typenameenable_if_convertible<F2,UnaryFunction>::type*=0//expo-sitiononly

);

Returns:Aninstanceoftransform_i torwithm_finitializedtot.functor()and

m_i torinitializedtot.base().

Requires:OtherI torisimplicitlyconvertibletoI tor.UnaryFunctionfunctor()const;

Returns:m_f

I torconst&base()const;

Returns:m_i torreferenceoperator*()const;

Returns:m_f(*m_i tor)transform_i tor&operator++();

Effects:++m_i tor

Returns:*this

transform_i tor&operator--();

Effects:--m_i tor

Returns:*this

temte<classUnaryFunction,classI tor>transform_i tor<UnaryFunction,I tor>make_transform_i tor(I torit,UnaryFunctionfun);

Returns:Aninstanceoftransform_i tor<UnaryFunction,I tor>withm_fini-tializedtofandm_i torinitializedtox.

temte<classUnaryFunction,classI tor>transform_i tor<UnaryFunction,I tor>make_transform_i tor(I torit);

Returns:Aninstanceoftransform_i tor<UnaryFunction,I tor>withm_fde-faultconstructedandm_i torinitializedtox.

Example

Thisisasimpleexampleofusingthetransformitorsclasstogenerateitorsthatmultiply(oraddto)thevaluereturnedbydereferencingtheitor.Itwouldbecoolertouselambdalibraryinthiample.

intx[]={1,2,3,4,5,6,7,8};

constintN=sizeof(x)/sizeof(int);

typedefboost::binder1st<std::multiplies<int>>Function;

typedefboost::transform_i tor<Function,int*>doubling_i tor;

doubling_i tori(x,boost::bind1st(std::multiplies<i