On Sun, Mar 30, 2008 at 11:28 PM, David Abrahams <dave@boost-consulting.com> wrote:
on Fri Mar 28 2008, Steven Watanabe <watanabesj-AT-gmail.com> wrote:
AMDG
Giovanni Piero Deretta wrote:
That is, something like this is actually possible:
void foo () { int i = lambda // introduce formal parameter names [ _<class left>(), _<class right>() ] // now use them! [_<left>() + _<right>()] // actual parameters values ( 10, 20 ); }
The _<...>() looks a bit clumsy, but it might be actually usable.
I'd rather not use _. arg sound better. lambda<class left, class right>(arg<left>() + arg<right>())
lambda<args(class left, class right)>(arg<left>() + arg<right>())
I actually like the short nondescriptive names. It's very rare that the semantic information in a descriptive name is more valuable than the syntactic economy of the existing syntax. Just compare the above to:
_1 + _2.
Which do you find clearer?
For simple expressions I agree 100%.
When the lambda expression is complicated enough that having real names is actually a win, I am usually inclined to write a separate, named function (object), anyway.
For boost lambda I somewhat agree. Complex expressions unfortunately become too compile time heavy. OTOH, refactoring a lambda on a separate function object is a pain if you have to figure out the result of a complex composition of polymorphic function objects (result_of helps only to a point). For example, what is the result of: filter_view(reverse_view(mapped_view(range, op)), filter) (I often find much more complex expressions in my code). Also,what about MPL? As it deals only with types, the named parameter syntax is very light, and I have found out that one can write very complex mpl expressions with very little need for refactoring.
Wow. This is awesome. You'd probably better reference the standard (3.3.1/5) since most people will look at this and be surprised to find that it's legal. (I certainly was)
Not so fast. It's legal outside a function, but inside a function
"class A"
refers to a local class of the function, which isn't a legal template parameter. You might try the following at http://www.comeaucomputing.com/tryitout/ [...]
I did (see my other message). Yes, unfortunately the trick is illegal at function scope at lest untill C++0x. Which limits a lot its usefulness. -- gpd