From: Rocky Bernstein <rocky.bernstein@...>
Date: 2008-03-13T12:21:24+09:00
Subject: Ruby 1.8.6 binding value after "if" expression evaluation

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Here's another trace hook weirdness that I've encountered.

Consider this program and its output:

def trace_func(event, file, line, id, binding, klass, *)
  printf("%s:%d (%s) x=%s\n", file, line, event, eval("x", binding))
end
set_trace_func method(:trace_func).to_proc
x=5
x=6.2 if x=6.1
x=7


$ ruby bug2.rb
bug2.rb:6: warning: found = in conditional, should be ==
bug2.rb:5 (line) x=
bug2.rb:6 (line) x=5
bug2.rb:6 (line) x=5
bug2.rb:7 (line) x=6.2

Why does x appear to have value 5 the second time on line 7 rather than 6.1?


Looking at eval.c what's supposed to happen (I think) is that the trace hook
is called before the expression (x=6.1) is evaluated and then called before
the assignment "x=6.2" in which case it should have value 6.1, not 5.

Can anyone explain why this happens?

Again this is ruby 1.8.6

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Here&#39;s another trace hook weirdness that I&#39;ve encountered.<br><br>Consider this program and its output:<br><br><span style="font-family: courier new,monospace;">def trace_func(event, file, line, id, binding, klass, *)</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">&nbsp; printf(&quot;%s:%d (%s) x=%s\n&quot;, file, line, event, eval(&quot;x&quot;, binding))</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">end</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">set_trace_func method(:trace_func).to_proc</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">x=5</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">x=6.2 if x=6.1</span><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">x=7<br><br><br>$ ruby bug2.rb<br>bug2.rb:6: warning: found = in conditional, should be ==<br>
bug2.rb:5 (line) x=<br>bug2.rb:6 (line) x=5<br>bug2.rb:6 (line) x=5<br>bug2.rb:7 (line) x=6.2<br><br><font face="arial,sans-serif">Why does x appear to have value 5 the second time on line 7 rather than 6.1? <br><br>Looking at eval.c what&#39;s supposed to happen (I think) is that the trace hook is called before the expression (x=6.1) is evaluated and then called before the assignment &quot;x=6.2&quot; in which case it should have value 6.1, not 5.<br>
<br>Can anyone explain why this happens? <br><br>Again this is ruby 1.8.6 <br></font></span>

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