Extend the call site default argument expansion mechanism?

[rikki cattermole]

On 11/05/2018 2:15 AM, Yuxuan Shui wrote:
> So in D I can use default argument like this:
> 
> int f(int line=__LINE__) {}
> 
> And because default argument is expanded at call site, f() will be 
> called with the line number of the call site.
> 
> This is a really clever feature, and I think a similar feature can be 
> useful in other ways.
> 
> Say I need to construct a bunch of data structure that takes an 
> Allocator argument, I need to do this:
> 
> ...
> auto alloc = new SomeAllocator();
> auto data1 = new DataStructure(..., alloc);
> auto data2 = new DataStructure(..., alloc);
> auto data3 = new DataStructure(..., alloc);
> ...
> 
> This looks redundant. But if we have the ability to define more special 
> keywords like __LINE__, we can do something like this:
> 
> ...
> // constructor of DataStructure
> this(Allocator alloc=__ALLOC__) {...}
> ...
> auto alloc = new SomeAllocator();
> define __ALLOC__ = alloc;
> // And we don't need to pass alloc everytime
> ...
> 
> Is this a good idea?

Bad idea, too much magic.