Ingo Blechschmidt wrote:
>    # No problem:
>    my $data = BEGIN {
>      my $fh = open "some_file" err...;
>      =$fh;
>    };
>  
>    # Problem;
>    my $fh = BEGIN { open "some_file" err... };
>    # Compile-time filehandle leaked into runtime!
>    say =$fh;
[...]
>  * There's a boolean property may_leak_into_runtime every object has,
>    with a default of true.
>    BEGIN and CHECK then check if the object they're about to return has
>    .may_leak_into_runtime set to false -- if that's the case, die:
>  
>    class MyClass does may_leak_into_runtime(false) {
>      method get_some_value () {...}
>    }
>  
>    my $foo = BEGIN { MyClass.new }.get_some_value; # really means
>    my $foo = BEGIN {
>      my $result = MyClass.new;
>      $result.may_leak_into_runtime ?? $result :: die "...";
>    }.get_some_value;
>  
>    Pro: Great flexibility, easy to use

unfortunately, even though I really like that solution, I found a
scenario where it'll fail:

    my $foo = BEGIN {
        my $fh = open "some_file";
        # $fh.may_leak_into_runtime is 0, so if we return $fh
        # the compiler would throw an exception.
        # But, instead, we create a closure:
        my $code = { =$fh };
        # $code.may_leak_into_runtime is 1, as Code is not an IO.
        # So, this won't fail at compile-time.
    };
    say $foo();
    # Compiler isn't able to catch this error at compile-time.

Maybe we should just hardcode the filehandles-leaking-into-runtime case
in the compiler? And, if the compiler can't detect the problem at
compile-time, just throw a runtime exception?

    my $fh = BEGIN { open "some_file" };
    =$fh;  # "Can't readline() on unopened filehandle leaked
           # from compile-time into runtime, try to..."

Opinions?


--Ingo

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