«if» imposes a scalar context on the condition. That means the conditional expression is incapable of returning a list. The list can't possibly be empty, not empty, true or false if it doesn't even exist.

A hash slice in scalar context returns the last element, so

if (@x{1,2})
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is the same as

if ($x{2})
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The following operators evaluate EXPR in list context and count the number of returned values:

if (@{[ EXPR ]})    # Array

if (map 1, EXPR)    # map

if (grep 1, EXPR)   # grep

if (() = EXPR)      # List assignment

if (count(EXPR))    # External function such as
                    #    sub count { 0+@_ }
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