[boost] Re: Interesting Boost Implementation Details?

From: Larry Evans (cppljevans_at_[hidden])
Date: 2005-01-06 18:24:12

On 01/06/2005 02:29 PM, David Abrahams wrote:
> 
> * ... your ideas here ... :)
> 

I've had some trouble understanding how placeholders and lambda
expressions work.  Specifically, I've wondered why,
when a template is instantiated with _1, _2, ...,
that the instantiation doesn't produce some sort of error
messages.  For instance, if the template requires one of
its arguments to satisfy some requirement, then how could
_1 or _2 satisfy such a requirement since they couldn't
know about it?  Then I'm wondering about the complexity
when the lambda is applied to an argument.  Wouldn't each
_1 have to be replaced by the actual argument, and wouldn't
this require somehow parsing the template expression?
I'm thinking I'll have to experiment to see how it's done.
I have looked a little at the code but I can't figure
it out yet.  Maybe you're audience, if they're similarly
curious, would like to have those questions answered.