D as a prototyping language (for C/C++ projects)

[Andrei Alexandrescu]

On 2/28/13 11:36 AM, David Nadlinger wrote:
> On Thursday, 28 February 2013 at 15:51:02 UTC, Andrei
> Alexandrescu wrote:
>> On 2/28/13 10:49 AM, Andrei Alexandrescu wrote:
>>> On 2/28/13 10:24 AM, Jacob Carlborg wrote:
>>>> That is not my idea of "tap". This is my idea of "tap":
>>>>
>>>> Object (func) (Object o)
>>>> {
>>>> func(o);
>>>> return o;
>>>> }
>>>
>>> I know. I think my tap is better than your tap.
>>
>> ... and closer in intent to Ruby's tap as I understand it from reading
>> http://ruby-doc.org/core-2.0/Object.html#method-i-tap
>
> Ruby's tap just applies the passed block to the object it is
> called on. I am not quite sure how your range idea comes into
> play here?
>
> David

Oh, I misunderstood the example at 
http://ruby-doc.org/core-2.0/Object.html#method-i-tap:

(1..10)                .tap {|x| puts "original: #{x.inspect}"}
   .to_a                .tap {|x| puts "array: #{x.inspect}"}
   .select {|x| x%2==0} .tap {|x| puts "evens: #{x.inspect}"}
   .map { |x| x*x }     .tap {|x| puts "squares: #{x.inspect}"}

It eagerly prints the entire range, then eagerly prints the entire 
array, then eagerly the entire filtered range, then eagerly the entire 
map result.

I thought it works lazily, and I think in D it should (otherwise it 
would be e.g. useless with an input range). So the D translation would be:

iota(1, 10)
   .tap!(a => writeln("original: ", a))
   .filter!(a => a % 2 == 0)
   .tap!(a => writeln("filtered: ", a))
   .map!(a => a * a)
   .tap!(a => writeln("squared: ", a));

This will produce output interleaved, so it's semantically different.

I've used something similar to "tap" in a streaming-based library for 
machine learning I worked on as a grad student. It's been instrumental 
for data analysis and debugging. This conversation reminded me of it.

So my thought on the subject - I don't care much for

T tap(alias func)(T x) { func(x); return x; }

It's the kind of chaff that doesn't do any real work and only dilutes 
the value of a library, but I do think a tap tapping into a range does 
real work and would be a valuable addition.


Andrei