From: Paul Brannan <pbrannan@...>
Date: 2001-10-03T23:52:38+09:00
Subject: [ruby-talk:22010] Re: Backtrace with eval

On Wed, 3 Oct 2001, ts wrote:
>  Now try (to see the difference)
>
>  eval "bar", nil, "(eval)"

Interesting, this is also the same (since "(eval)" is the default value
for the third argument).  However,

  eval "bar", nil, "eval"

is different.  eval seems to treat "(eval)" as a special case (eval.c,
line 4912):

            if (strcmp(file, "(eval)") == 0) {
                if (ruby_sourceline > 1) {
                    errat = get_backtrace(ruby_errinfo);
                    err = RARRAY(errat)->ptr[0];
                    rb_str_cat2(err, ": ");
                    rb_str_append(err, ruby_errinfo);
                }
                else {
                    err = rb_str_dup(ruby_errinfo);
                }
                errat = Qnil;
                rb_exc_raise(rb_exc_new3(CLASS_OF(ruby_errinfo), err));
            }

I'm not sure what the ruby_sourceline stuff is (perhaps you could
enlighten me?), but it seems that in the 'eval "bar", nil, "(eval)"' case,
the interpreter is only grabbing the line that the exception came from,
and using that in the exception string (rather than throwing a new
exception with the same backtrace plus the current calls stack).

Generally speaking, it is a bad idea to have undocumented special cases
like this.  Does Ruby have a rationale for doing this that I am not aware
of?

Paul