Re^2: Confused by Perl ternary operator

In this case, for arcane reasons, $param3 = @_ ? "Shift" : shift works as-is but is execution-order unsafe and if the expression were included in some other larger expression, could be quite a problem.

$param3 = @_ ? "Shift" : $_[0];
shift;
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The preceding example would be the safe way to write it.

Comment on Re^2: Confused by Perl ternary operator Select or Download Code

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Re^3: Confused by Perl ternary operator by ysth (Canon) on Aug 23, 2004 at 23:36 UTC
How is that execution-order unsafe? ?:'s first operand has to be evaluated before either the second or third. After writing the above, I checked perlop.pod, and technically you are correct. ?: isn't documented as short-circuiting, so perl potentially could evaluate the 2nd and 3rd operands before testing the first one. However, I believe that it is intended to short-circuit and will submit a patch to the doc. As an interesting side note, structures with else or elsif are implemented using condexpr (the ?: operator). That is, `if (foo) { bar } else { baz }` [download] is identical to `foo ? do { bar } : do { baz }` [download] so the short-circuiting of ?: is pretty guaranteed.	[reply] [d/l] [select]
Re^4: Confused by Perl ternary operator by diotalevi (Canon) on Aug 24, 2004 at 00:13 UTC
I was thinking that someone might use that expression that reads and writes to @_ inside another expression that depends on whether @_ has already been fetched or altered. ?: isn't just if/else, its an expression which can be used inside other expressions. `$join = ( @_ ? "Argument, the first" : shift ) . ( @_ ? "Argument, the second" : shift );` [download]	[reply] [d/l]