c++ - practice and discovery of Boost Type Erasure -


i reading boost type erasure , trying figure out potential usage. practice bit while reading tons of documentations topic (it looks big one). quoted area of application networking / exchanging data between client , server. can suggest other example or exercise can play bit library?

type erasure useful in extraordinary amount of situations, point may thought of fundamentally missing language feature bridges generic , object oriented programming styles.

when define class in c++, defining both specific type , specific interface, , these 2 things not need related. type deals data, interface deals transformations on data. generic code, such in stl, doesn't care type, cares interface: can sort container or container-like sequence using std::sort, long provides comparison , iterator interface.

unfortunately, generic code in c++ requires compile time polymorphism: templates. doesn't things cannot known until runtime, or things require uniform interface.

a simple example this: how store number of different types in single container? simplest mechanism store of types in void*, perhaps type information distinguish them. way recognize of these types have same interface: retrieval. if make single interface retrieval, specialize each type, if part of type had been erased.

any_iterator useful reason this: if need iterate on number of different containers same interface, need erase type of container out of type of iterator. boost::any_range subtle enhancement of this, extending iterators ranges, basic idea same.

in short, time need go multiple types similar interface single type single interface, need form of type erasure. runtime technique equates compile time templates.


Comments

Post a Comment

Popular posts from this blog

c# - Send Image in Json : 400 Bad request -

from android trying send image class of data, iis webservice. (c#) the problem 400 bad request . the image being encoded base64 . , placed json rest of class elements. my guess base64 not valid inside json. server not understand it. if set string "" , post accepted fine. so question is, how make base64 valid within json array? ( tried url.encode no success). or how should send image android webservice? gson gson = new gson(); string json = gson.tojson(record); // record has param { string base64photo } how big image? i'm pretty sure surpassing iis json size limit (default 4 mb). check http://geekswithblogs.net/frankw/archive/2008/08/05/how-to-configure-maxjsonlength-in-asp.net-ajax-applications.aspx or http://www.webtrenches.com/post.cfm/iis7-file-upload-size-limits good luck!
Read more

javascript - addthis share facebook and google+ url -

i attempting use addthis create simple url shares whichever current page user on when click share button. of right now, have twitter working. when user clicks, able see url populated in tweet box. when user clicks facebook or google+, url doesn't seem show in share box. <ul class="addthis_toolbox addthis_default_style "> <li><a class="addthis_button_facebook"><img src="/img/facebook-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_twitter"><img src="/img/twitter-social.png" width="20" height="20" border="0" alt="share" /></a></li> <li><a class="addthis_button_google_plusone_share"><img src="/img/google-social.png" width="20" height="20" border="0" alt="s...
Read more

ios - Show keyboard with UITextField in the input accessory view -

i have buttona , when buttona clicked, want keyboard show uitextfield in inputaccessoryview. there way have keyboard show manually , set inputaccessoryview without having uitextfield initially? thanks. you cannot summon keyboard without object can become first responder. there 2 ways work around: subclass uiview , implement uikeyinput protocol in it. example: in .h file: @interface inputobject : uiview<uikeyinput> @property (nonatomic, copy) nsstring *text; @property (nonatomic, strong) uiview *inputaccessoryview; // must override inputaccessoryview , since it's readonly default @end in .m file, implement protocol: - (bool)canbecomefirstresponder { return yes; } - (bool)hastext { return [self.text length]; } - (void)inserttext:(nsstring *)text { nsstring *selftext = self.text ? self.text : @""; self.text = [selftext stringbyappendingstring:text]; [[nsnotificationcenter defaultcenter] postnotificationname:kinputobjec...
Read more