c++ - Why is there no std::is_transparent equivalent for unordered containers? -

-

c++14 introduces compare::is_transparent equivalent find operations in associative containers.

template< class k > iterator       find( const k& x ); template< class k > const_iterator find( const k& x ) const;

finds element key compares equivalent value x. overload participates in overload resolution if qualified-id compare::is_transparent valid , denotes type. allows calling function without constructing instance of key

since there no longer temporary instance of key constructed, these can more efficient.

there not seem equivalent unordered containers.

why there no compare::key_equal / compare::hash_equal?

i imagine relatively simple allow efficiently looking of, eg, string literals in unordered containers?

template<> struct hash<string> {     std::size_t operator()(const string& s) const      {         return ...;     }     // hash_equal=true allows hashing string literals     std::size_t operator()(const char* s) const     {         return ...;     } };

if watch grill committee video cppcon, explain why stuff happens: nobody fought it.

c++ standardized committee committee requires input community. has write papers, respond criticism, go meetings, etc... feature can voted on. committee doesn't sit there inventing language , library features. discusses , votes on brought forward it.


Comments

Post a Comment

Popular posts from this blog

javascript - Chart.js (Radar Chart) different scaleLineColor for each scaleLine -

-
Image
i try , create radar chart using chart.js has various colours each scaleline, or coloured between scalelines. wondering if possible? from: to: i have working graph, though there doesn't seem method change individual scale lines. kind regards leigh you can extend radar chart type this, so chart.types.radar.extend({ name: "radaralt", initialize: function (data) { chart.types.radar.prototype.initialize.apply(this, arguments); var originalscaledraw = this.scale.draw; var ctx = this.chart.ctx; this.scale.draw = function () { var linewidth = this.linewidth; // bypasses line drawing in originalscaledraw this.linewidth = linewidth; originalscaledraw.apply(this, arguments); ctx.linewidth = this.linewidth; var scale = this; // draw chart.helpers.each(scale.ylabels, function (label, index) { // color of ...
Read more

apache - Error with PHP mail(): Multiple or malformed newlines found in additional_header -

-
suddenly have started receiving above error without changes having been made script. host 1and1 (i know...) the script still works fine on different server, , suspicion there must have been server config change has lead this, although hosts plead ignorance. there's no information on above error @ in google can find - have ideas? server running apache if helps. had similar problem. came out of blue. no php code changed. what changed: php upgraded 5.5.25-1 5.5.26. a security risk in php mail() function has been fixed , newlines in additional_headers allowed no more. because newlines mean: starts email message (and surely don't want inject newlines through headers followed evil message). what have worked fine, e.g. having newlines after headers or passing whole message additional_headers , function no more. solution : sanitize headers. no multiple newlines in additional_headers argument. these count "multiple or malformed newlines":...
Read more

java - Android – MapFragment overlay button shadow, just like MyLocation button -

-
Image
i'm struggling add shadow custom overlay button on google map. goal make custom button google's mylocation button. here's how app looks now: layout.xml <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" xmlns:map="http://schemas.android.com/apk/res-auto" android:layout_height="match_parent" android:layout_width="match_parent" style="@style/apptheme"> <fragment android:layout_width="match_parent" android:layout_height="match_parent" android:id="@+id/map" tools:context=".mapsactivity" android:name="com.google.android.gms.maps.supportmapfragment" android:layout_alignparentend="true" android:layout_alignparentstart="true" android:layout_alignparentbottom="true" ...
Read more