Hi, after upgrading to 1.0.62 I got following error when using sys::Test.verifyErr:

class MyTest : Test {
  Void testSmth() {
    verifyErr(ParseErr#) { Int.fromStr("@#!") }
  }
}


[~/Dropbox/ws/xored/spectre/src/test] fan MyTest.fan 
/Users/prokopov/Dropbox/ws/xored/spectre/src/test/MyTest.fan(3,32): Not a statement
ERROR: cannot compile script

It was working in 1.0.61, and code I used here was copied directly from http://fantom.org/doc/sys/Test.html#verifyErr

Thanks!

That is related to the static new constructor change. Now they are true constructors, and the compiler doesn't allow a constructor call with it being assigned to something or used as a parameter. What I do is just assign to throw away local variable:

x := Int.fromStr("@#!")

Thanks for the answer, Brian.

Why cannot be constructors used as a return value?

And, I think, you should also update example in the docs to be compileable?

Why cannot be constructors used as a return value?

Not sure what you mean, they are! They return the object you've just constructed! It's just that you currently have to do something with that object - and not leave it hanging.

What I do is just assign to throw away local variable: x := Int.fromStr("@#!")

Hmm, when F4 gets updated (fingers crossed real tight!) it may introduce warnings for unused variables, like the one above. Maybe call some innocuous method instead, like

Int.fromStr("@#!").toStr

Other than it's bad programming to have contructors do work, what's the reason for the Fantom compiler to out right disallow it, and force assignment or usage?

And, I think, you should also update example in the docs to be compileable?

I agree, the docs are the Fantom Bible and to help out new comers (like me!), they should always be correct, complete and upto date.

I have already changed the documentation.

What Fantom disallows is using a constructor as a complete statement. For example you can't use a literal 71 as a statement, nor can you use Date("2010-01-02") either. That expression has to be assigned to a variable, used as a parameter, or returned as result of a function or method.

As a general policy just constructing an object and not doing anything with it should be a side-effect free operation that is indeed a bug. This is especially tricky in certain places in Fantom where this compiler error is very useful. Consider:

// this works
GridPane { Label { text="hi" }, }

// this is broken and will report a compiler error because 
// you aren't actually using the Label instance
GridPane { Label { text="hi" } }

When we are testing that a function throws an exception, we are actually interested in the side effect, but we have to do something with the result to please the compiler.

Fair enough - but don't you mean:

// this works
x: = GridPane { Label { text="hi" }, }

:)