I posted this question a few months ago, but I got pulled away to deal with more pressing work issues. So here it goes again: I'm trying to use lambda expressions to implement 'twice'. So I came up with typedef mpl::apply<_1, mpl::apply<_1, _2> > lambda_type; typedef lambda_type, int> result_type; When I look at result_type, I get is_same::type::value evaluates to true. I expected that is_same::type::value would evaluate to true. Why is my lambda expression 'lambda_type' only returning it's second argument?? ------------------------------------------- Manson: My philosophy is: Don't think. I don't believe in the mind that you think with and scheme with. I don't believe in words. Reporter: If you don't believe in words, why do you use so many of them? Manson: Words are symbols. All I'm doing is jumbling the symbols in your brain. Everything is symbolic. Symbols are just connections in your brain. Even your body is a symbol. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

--- David Abrahams wrote:

Lucio Flores writes:

...

I posted this question a few months ago, but I got pulled away to deal with more pressing work issues. So here it goes again:

I'm trying to use lambda expressions to implement 'twice'. So I came up with

typedef mpl::apply<_1, mpl::apply<_1, _2> > lambda_type;

typedef lambda_type, int> result_type;

Surely that doesn't compile(?) lambda_type is a type; you can't follow it with a template argument list.

You're right! .... But it did compile.... So what's the correct usage? Would it be: typedef mpl::apply< lambda_type, boost::add_pointer<_1>, int>::type result_type; ??? ------------------------------------------- Manson: My philosophy is: Don't think. I don't believe in the mind that you think with and scheme with. I don't believe in words. Reporter: If you don't believe in words, why do you use so many of them? Manson: Words are symbols. All I'm doing is jumbling the symbols in your brain. Everything is symbolic. Symbols are just connections in your brain. Even your body is a symbol. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

--- David Abrahams wrote:

Lucio Flores writes:

...

--- David Abrahams wrote:

...

Lucio Flores writes:

...

I posted this question a few months ago, but I got pulled away to deal with more pressing work issues. So here it goes again:

I'm trying to use lambda expressions to implement 'twice'. So I came up with

typedef mpl::apply<_1, mpl::apply<_1, _2> > lambda_type;

typedef lambda_type, int> result_type;

Surely that doesn't compile(?) lambda_type is a type; you can't follow it with a template argument list.

You're right! .... But it did compile....

What compiler ate that without complaint?

gcc version 3.3.5 20050117 (prerelease) (SUSE Linux 9.3) But the following wont compile: typedef mpl::apply<_1, mpl::apply<_1, _2> > lambda_type; typedef mpl::apply, int>::type answer_type; prog_3_6.cpp:22: error: no class template named `apply' in `struct lambda_type' prog_3_6.cpp:22: error: syntax error before `;' token ------------------------------------------- Manson: My philosophy is: Don't think. I don't believe in the mind that you think with and scheme with. I don't believe in words. Reporter: If you don't believe in words, why do you use so many of them? Manson: Words are symbols. All I'm doing is jumbling the symbols in your brain. Everything is symbolic. Symbols are just connections in your brain. Even your body is a symbol. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com