Generate command definitions that take arguments

I want to define a command \NewSmartOp such that:

\NewSmartOp \MYOP \myop

would produce the following code (or anything equivalent):

\makeatletter  \def\MYOP{\@ifstar\MYOP@star\MYOP@nostar}  \def\MYOP@star#1{\myop\!\left( #1 \right)}  \def\MYOP@nostar#1{\myop #1}\makeatother

I guess I need \expandafter and perhaps \csname … \endcsname but otherwise I have no clue how to generate these definitions, especially regarding how to form a new command name \MYOP@star from \MYOP, and also how to deal with these #1 that must be kept as-is in the produced definitions (by contrast with being expanded by the definition producing them).

Background (reading optional)

For a bit of context: when typing math I want to abstract from concrete syntax as much as possible. For instance, for cardinality of set S, perhaps I’d like it to be rendered as card S (with parentheses only when needed, e.g. card(S₁∪ S₂)), but perhaps at some point in the future I’d like to switch syntax to |S|. So I would define:

\DeclareMathOperator \card {card}\NewSmartOp \CARD \card % option 1%\newcommand* \CARD[1] {\left\lvert # \right\rvert} % option 2

after which

• I might use the operator directly (low-level, my TeX typing reflects the concrete syntax): \card S or \card(S);
• but I’d rather use a command with an argument to which I defer the concrete syntax (high-level, my TeX typing reflects the abstract syntax tree): \CARD {S}.

This ideal seems hard to achieve fully because I cannot(?) find out automatically when parentheses are needed, so the compromise I adopted is to have starred versions of these “smart operators” add parentheses: \CARD* {S_1 \cup S_2}.