C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  how to read boost::lambda expression          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Fei Liu Guest Posted: Thu May 11, 2006 1:21 pm    Post subject: how to read boost::lambda expression I tried the boost::lambda library in the following test code and I found it difficult to parse/interpret what the code does in a sense how a compiler parse/interpret it. For example, when both a compiler and I see 'a=b+c' as assign the result of addition to a 3rd number in a straightfoward maner but the lambda expressions are in a different league. How does a compiler parse/interpret the lambda statements in the following code? The comments are mine. Thanks for your help. #include <iostream> #include <boost/lambda/lambda.hpp> #include <boost/function.hpp> int main(){ using namespace boost::lambda; // this executes an unamed function with 3 arguments? (std::cout << _1 << " " << _3 << " " << _2 << "!\n") ("hello", "friend", "my"); // this defines a function but there is no function body { ... } ? boost::function<void(int, int, int)> f= std::cout << _1 << "*" << _2 << "+" << _3 << "=" << _1*_2+_3 << "\n"; f(1,2,3); f(3,2,1); } [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Carl Barron Guest Posted: Fri May 12, 2006 12:21 am    Post subject: Re: how to read boost::lambda expression In article <1147290951.170654.251440 (AT) i39g2000cwa (DOT) googlegroups.com>, Fei Liu <fei.liu (AT) gmail (DOT) com> wrote: Quote: I tried the boost::lambda library in the following test code and I found it difficult to parse/interpret what the code does in a sense how a compiler parse/interpret it. For example, when both a compiler and I see 'a=b+c' as assign the result of addition to a 3rd number in a straightfoward maner but the lambda expressions are in a different league. How does a compiler parse/interpret the lambda statements in the following code? The comments are mine. Thanks for your help. lambd uses a techinque of template metaprogramming called expression templates to have the complier 'compute' a functor to execute the given expression. Perhaps the pdf at mrl.nyu.edu/~mkg/professional/programming/expr_templates.pdf might explain the technique as it is a bit complicated for a newsgroup message... [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Niek Sanders Guest Posted: Fri May 12, 2006 12:21 am    Post subject: Re: how to read boost::lambda expression Fei Liu wrote: Quote: I tried the boost::lambda library in the following test code and I found it difficult to parse/interpret what the code does in a sense how a compiler parse/interpret it. For example, when both a compiler and I see 'a=b+c' as assign the result of addition to a 3rd number in a straightfoward maner but the lambda expressions are in a different league. How does a compiler parse/interpret the lambda statements in the following code? The comments are mine. Thanks for your help. Check out the paper on "Expression Templates" written by Todd Veldhuizen: http://osl.iu.edu/~tveldhui/papers/Expression-Templates/exprtmpl.html The book "C++ Templates: The Complete Guide" by Vandevoorde and Josuttis also has a chapter (#1 on the topic. I haven't read this book yet, so I can't say anything about the quality of their exposition. - Niek Sanders http://www.cis.rit.edu/~njs8030/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Fei Liu Guest Posted: Fri May 19, 2006 10:21 am    Post subject: Re: how to read boost::lambda expression Carl Barron wrote: Quote: In article <1147290951.170654.251440 (AT) i39g2000cwa (DOT) googlegroups.com>, Fei Liu <fei.liu (AT) gmail (DOT) com> wrote: I tried the boost::lambda library in the following test code and I found it difficult to parse/interpret what the code does in a sense how a compiler parse/interpret it. For example, when both a compiler and I see 'a=b+c' as assign the result of addition to a 3rd number in a straightfoward maner but the lambda expressions are in a different league. How does a compiler parse/interpret the lambda statements in the following code? The comments are mine. Thanks for your help. lambd uses a techinque of template metaprogramming called expression templates to have the complier 'compute' a functor to execute the given expression. Perhaps the pdf at mrl.nyu.edu/~mkg/professional/programming/expr_templates.pdf might explain the technique as it is a bit complicated for a newsgroup message... Thank you both for your links, they are actually identical articles in different format. They did explain some of the techniques used behind lambda. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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