Just like "FOO + BAR" doesn't return "FOO" or "BAR", "FOO = BAR" doesn't necessarily return "FOO" or "BAR". A list assignment in scalar context returns the number of values returned by its RHS.

In detail,

"($x,$y) = a()" is a list assignment, and it is being evaluated in scalar context (from the if()). A list assignment in scalar context returns the number of values returned by its RHS. In this case, that's 2.

"(undef,undef) = a()" is a list assignment, and it is being evaluated in scalar context (from the if()). A list assignment in scalar context returns the number of values returned by its RHS. In this case, that's 2.

"a()" is a function call, and it is being evaluated in scalar context (from the if()). A function called in scalar context evaluates its return expression in scalar context, so "undef, undef" is evaluated in scalar context. The list/comma operator in scalar context evaluates each operand in turn and returns the last value. In this case, that's undef.

"undef, undef" is being evaluated in scalar context (from the if()). The list/comma operator in scalar context evaluates each operand in turn and returns the last value. In this case, that's undef.

In reply to Re: Can't understand function returning undefs by ikegami
in thread Can't understand function returning undefs by rg0now

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