assert with body

[gavinking]

In #891 it was proposed that we could support stuff like this:

assert (exists length, nonempty sequence, length>0) {
    return null;
}

Even though #891 is now implemented, there may still be value in that. I personally find it to be a more pleasing and more powerful way to write "guards".

[lucaswerkmeister]

I still think it’s much clearer with else, i. e.

assert (exists length, nonempty sequence, length>0) else {
    return null;
}

[FroMage]

So the difference with if is that the new values scope extends to the end like normal assert, and the difference with normal assert is the failure code that can be customised rather than just throw, right?

[gavinking]

Well the really big difference is that to write the above with if, I would have to write:

if (!exists length) {
    return null;
}
if (!nonempty sequence) {
    return null;
}
if (length<=0) {
    return null;
}

Which is significantly worse.

[quintesse]

I can't help but intensely dislike this, but I don't see any other option since we decided a long time ago to have this , notation in conditions.

Honestly, I agree with @quintesse. I think a better aproach would be to allow people to put ! before conditional thingies:

if!(exists bar, foo())
{
    assert(false);
}
bar.baz();

Same for while!(), and assert!()...

But also, I agree with @gavinking that these "guard" thingles are not very ceylonic. If you end up with a bunch of ifs guarding your actual code, then just put your code actually inside the if block...

if(!exists foo) { return(null); }
if(!exists bar) { return(null); }
if(!exists baz) { return(null); }
// actual code

becomes

if!(exists foo, exists bar, exists baz)
{
    // actual code
}
else
{
    return(null);
}

[bjansen]

Oh so now I could rewrite this Java code:

if (foo == null || foo == bar) {
    return;
}

to a nice

assert(exists foo, foo != bar) {
    return;
}

instead of the ugly

if (foo?.equals(bar) else true) {
    return;
}
assert(exists foo);

I like that 👍

[RossTate]

I agree with @lucaswerkmeister, the else is necessary to make this clear to people not familiar with the feature.

[luolong]

I somewhat dislike the else after the assert condition.

Although, I can see how it makes the it more explicit when the block is being invoked...

I would however add an additional condition to the assertion failure block that it has to definitely return.

Otherwise it is indistinguishable from if