From -6805407325937466424 X-Google-Thread: f78e5,2feb33bcd45033ce X-Google-NewGroupId: yes X-Google-Attributes: gid7894ca11fe,domainid0,public,usenet X-Google-Language: ENGLISH,ASCII Path: g2news1.google.com!news2.google.com!npeer03.iad.highwinds-media.com!news.highwinds-media.com!feed-me.highwinds-media.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 20 Sep 2010 01:30:01 -0500 Return-Path: X-Hash: SCt|e0341dae70905199d9c3d4443eb33310f92f38fb|05c1ff68428dd73191e972f83f937250 X-Countries: United States X-SMTP-From: accepted assassin.cs.rpi.edu [128.113.126.17] (assassin.cs.rpi.edu) {United States} DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=cs.rpi.edu; h=date :to:sender:message-id:from:subject:references:content-type; s= default; i=128.113.126.17@cs.rpi.edu; t=1284964032; x= 1285568832; l=1639; bh=NAt2mp0P759r22My48C/Dld9gZk=; b=XYXY2JLOh gPWEMUqA/hdwtZ8EM8ZhT66KUYw9ILnOvapw0ywUzzWtdhRwSVfvE5fvHqkHIxbZ rvi1hI5peYJWlL46TG8ndhRIQLEpf1cWOcP9eX54ReNLcm4FqtMKG3tRkXAaCidI S8Gz5A/j60GvVpMWA3PubsJGDbUIXdLSGE= DomainKey-Signature: a=rsa-sha1; c=nofws; d=cs.rpi.edu; h=date:to:sender :message-id:from:subject:references:content-type; q=dns; s= default; b=Bn9HcYFlFks7NfsPsrU1Zvkp+V7X4m3Q0R8lP6DsczYVLRsIQ7fJB 4DiTDhs5Uu+wL7zd1IvK0n1p/iJa3qBUSLIpo4NKoDGBkUvFInmVG3kdj+ODXvLH 5Y7gfZ/CJATJmnDCq2avzRHlB219LY1/e90sAtaRD549OY5PQYEuc0= X-Spam-Report: Spam Report from cliffclavin.cs.rpi.edu (SA:3.2.5): -1.8 ALL_TRUSTED Passed through trusted hosts only via SMTP 3.4 HEADER_SPAM Bulk email fingerprint (header-based) found -0.9 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.2 SARE_HEAD_HDR_APPROV Message headers used which identify spam 0.0 AWL AWL: From: address is in the auto white-list X-Spam-Info: 0.9, local; ALL_TRUSTED,AWL,BAYES_00,HEADER_SPAM,SARE_HEAD_HDR_APPROV X-Spam-Scanned-By: cliffclavin.cs.rpi.edu using SpamAssassin 3.2.5 X-Virus-Scanned-By: cliffclavin.cs.rpi.edu To: (Usenet) Sender: std-c++-request@ruralroute.cs.rpi.edu Approved: james.dennett@gmail.com Message-ID: Newsgroups: comp.std.c++ From: =?ISO-8859-1?Q?Daniel_Kr=FCgler?= Subject: Re: Bracket, equals, bracket? Organization: http://groups.google.com References: Content-Type: text/plain; charset=ISO-8859-1 X-Original-Date: Sun, 19 Sep 2010 22:53:19 -0700 (PDT) X-Submission-Address: std-c++@netlab.cs.rpi.edu X-Scanned-By: MIMEDefang 2.67 on 128.113.126.25 Date: Mon, 20 Sep 2010 01:27:12 CST Lines: 49 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-E7fclZf8WIhmyab9IuZffRBDMDEgwpW38MG6aXjZwpl1GJ6EbrlBrLURRY3vANYYQEl8dZr0prOSOrg!ov6ohDfxVox2YSEypv7MdDXbglHsprpWnsxhSjYq3aYaspnfpYpwEzu8oO2DQdVtZhx9PkreqwyS!WVIVmRa0N13CDpzD78d0I/hXgfI= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Xref: g2news1.google.com comp.std.c++:3019 On Sep 20, 2:13 am, Duncan Smith wrote: > In this months DDJ Herb Sutter writes some code like: > > class AsyncLogFile { > public: > void write( string str ) { a.Send( [=] { log.write( str ); } ); } > > My question is what does [=] mean, I thought square brackets were for > indexing arrays unless maybe the operator[] is overloaded, but then a > google codesearch shows other uses of [=], does it have a special or > common meaning? The meaning of [=] makes only sense in the whole context of a so-called lambda-expression, which is a new expression form in C++0x and defines a lambda-closure, which is a compiler-generated class-type functor. The whole lambda-expression above is [=] { log.write( str ); } and defines a closure type which is - roughly said - constructed like this: struct __ { std::string s; __(const std::string& s) : s(s) {} void operator()() { log.write( str ); } }; assuming that log is a global-scope variable. Such a closure *captures* local variables, and the = within the [] defines the default-policy, how this is done. If this is =, all local variables are captured by *copy* (i.e. the string s was copied. The other alternative for the default capture is "by-reference", where you use the token & instead of = within the [] token. HTH & Greetings from Bremen, Daniel Kr�gler -- [ comp.std.c++ is moderated. To submit articles, try just posting with ] [ your news-reader. If that fails, use mailto:std-c++@netlab.cs.rpi.edu] [ --- Please see the FAQ before posting. --- ] [ FAQ: http://www.comeaucomputing.com/csc/faq.html ]