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echo("Normal variables");
echo(is_undef(a)); //no warning
b="hallo";
echo(is_undef(b));
c=undef;
echo(is_undef(c));
echo(a); //warns
echo(b);
echo(c);
echo("Test with scopes");
if(true){
echo(is_undef(b));
d=true;
echo(is_undef(c));
echo(d);
}
echo(is_undef(d));
echo(d);
echo("Special variables");
echo(is_undef($a)); //no warning
$b=132465;
echo(is_undef($b));
$c=undef;
echo(is_undef($c));
echo($a);
echo($b);
echo($c);
echo("constants resulting in true");
echo(is_undef(undef));
echo("constants resulting in false");
echo(is_undef("Test"));
echo(is_undef(123456));
echo("constants resulting in undef");
echo(is_undef());
echo(is_undef("Test",123));
echo(is_undef(123,456));
echo("functions resulting in true");
echo(is_undef(len("test","upps")));
echo(is_undef(is_undef()));
echo("functions resulting in false");
echo(is_undef(sin(1)));
echo(is_undef(len("test")));
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