about lambdas

[Maxim Fomin]

On Wednesday, 2 January 2013 at 21:00:10 UTC, Michael wrote:
> R  With(I, R)(I o, R function (I) fun)
> {
> 	static if(isAssignable!(I, typeof(null)))
> 		return o is null ? null : fun(o);
> 	else
> 		return fun(o);
> }
>
> class Person
> {
> 	private
> 	{
> 		string  _name;
> 		Address _address;
> 	}
>
> 	@property
> 	{
> 		string name() { return	_name; }
> 		void   name(string v) { _name = v; }
>
> 		Address address() { return _address; }
> 		void	address(Address v) { _address = v; }
> 	}
> }
>
> in main function
> ----------------
> foreach(p; persons)	
> 	p.With((Person x) => x.address); // works
>
> but
> ----------------
> foreach(p; persons)	
> 		p.With(x => x.address); // error
>
> nullcheck.d(89): Error: template maybe.With does not match any 
> function template
>  declaration. Candidates are:
> maybe.d(20):        maybe.With(I, R)(I o, R function(I) fun)
> nullcheck.d(89): Error: template maybe.With(I, R)(I o, R 
> function(I) fun) cannot
>  deduce template function from argument types !()(Person,void)
>
>
> Why?

The first one is a lambda function, the second one is a lambda 
template. Templates have type void.