unittest{...} as "free" code bolck

[spir]

On 04/13/2011 10:38 PM, Andrei Alexandrescu wrote:
> Similarly, it would be great if next to e.g.
> http://d-programming-language.org/phobos-prerelease/std_algorithm.html#setUnion
> there would be a "Try it now" button. Clicking on that button would open an
> overlay with an edit window. The edit window initially contains the example text:
>
> unittest
> {
>    int[] a = [ 1, 2, 4, 5, 7, 9 ];
>    int[] b = [ 0, 1, 2, 4, 7, 8 ];
>    int[] c = [ 10 ];
>    assert(setUnion(a, b).length == a.length + b.length);
>    assert(equal(setUnion(a, b), [0, 1, 1, 2, 2, 4, 4, 5, 7, 7, 8, 9][]));
>    assert(equal(setUnion(a, c, b), [0, 1, 1, 2, 2, 4, 4, 5, 7, 7, 8, 9, 10][]));
> }
>
> Then the user can change, compile, and run that program, to ultimately close
> the overlay and return to the documentation.

I recently started to realise a side-effect of the unittest feature is to 
provide D with "free code blocks", where one can just put any piece of code; 
code that could go on a module's top-level in a dynamic language.
Typically, this allows clean trials. Eg, does '/' perform euclidean division or 
true division, on integers / reals?

import std.stdio : writeln;
unittest {
     writeln("ints");
     writeln(2/2);
     writeln(3/2);
}
unittest {
     writeln("reals");
     writeln(2.0/2);
     writeln(3.0/2);
}
void main () {}

Sure, one can use main() for this. But unittest blocks are cleaner and allow 
structuration. In the same vein, unittests can be cleanly used to *demonstrate* 
language behaviour; for instance in tutorials, when showing issues like on 
D-leran, or for... bug reports.

Denis
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