Re: Testing lazy ranges in post-conditions

[Peter Alexander via Digitalmars-d]

On Monday, 24 November 2014 at 12:20:40 UTC, bearophile wrote:
Peter Alexander:
Should be able to do:

assert(result.save.all!(x => x < 10));

But iota's save isn't const, so you can't (that's a bug).

Mine was just an example of the general problem, another 
example:


import std.range, std.algorithm;

auto foo()
out(result) {
    assert(result.all!(b => b.length == 2));
} body {
    auto a = new int[10];
    return a.chunks(2);
}

void main() {}

Chunks.save should also be const, so result.save.{...} should 
work.

It becomes a real problem with input ranges, because you can't 
save them. That makes sense though, as there is no way to consume 
the result in a post-condition check that doesn't consume it. 
That's just a fact of life and a limitation of trying to verify 
mutable data.