No way!

The variable $whole is assigned the contents of the first set of capturing parentheses (the first (\d*)).
The variable $deci is assigned the contents of the second set of capturing parentheses (the first (\d+)).

/(?:(\d*)\.?(\d+))|(?:(\d+)\.?(\d*))/
    ^^^^^   ^^^^^
    Always  Always
    $whole  $deci
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Should the second alternation match — it never will — then $whole and $deci will be undef.