Re: [Boost-users] naming delayed variables string in boost lamdba

Subject: Re: [Boost-users] naming delayed variables string in boost lamdba
From: OvermindDL1 (overminddl1_at_[hidden])
Date: 2009-11-11 11:47:03

On Wed, Nov 11, 2009 at 9:24 AM, Roman Perepelitsa
<roman.perepelitsa_at_[hidden]> wrote:
> 2009/11/11 Emanuele Rocci <rocciemanuele_at_[hidden]>
>>
>> Hi All
>> I am getting familiar with boost::lambda.
>> Today I learnt about delayed variable and usage of boost::constant in
>> lambda expression.
>> Do you know why when I try to declare delayed variables for string like I
>> do below
>> the compiler gives me each time an error?
>> I tried the following
>> constant_type<const char*>::type _msg_a(constant("my msg"));
>> constant_type<const std::string>::type _msg_b(constant("my msg"));
>> constant_type<std::string>::type _msg_c(constant("my msg"));
>> If I use constant( "my msg" ) inside a boost lambda expression everything
>> is fine but I cannot declare correctly a delayed variable.
>> Do you know how to fix it or where I can get some details?
>> Thanks in advance
>> Mn
>
> Function objects generated by lambda have unspecified types. If you want to
> save them, use Boost.Function.
> #include <iostream>
> #include <boost/lambda/core.hpp>
> #include <boost/function.hpp>
> int main() {
> Â Â boost::function<const char*()> f = boost::lambda::constant("hello");
> Â Â std::cout << f() << std::endl;
> }

Or BOOST_AUTO (which will have lower overhead then Boost.Function).