TikZ: create a button to show something or not

Question

In some cases I create some (plenty of) buttons of the kind
defmyshow{1}%    1 'yes',    '0' no

and then ifnummyshow=1 .... fi
But I had to hear, this is not so correct. 
So: What is the correct (and unproblematic) way to create a button like that? Maybe something with pgfkeys?

documentclass[border=2mm, tikz]{standalone}
usepackage{tikz}
begin{document}
defmyshow{1}%    1 'yes',    '0' no

begin{tikzpicture}[]
coordinate[label=A](A) at (0,0);
coordinate[label=right:B](B) at (2,0);
coordinate[label=C](C) at (2,1);

ifnummyshow=1
draw[red, thick] (A) -- (B) -- (C) --cycle;
else% nothing
fi
end{tikzpicture}
end{document}

user231225 · Accepted Answer

You should under no circumstances try to overwrite commands like show, meaning. There is also no need for that. Apart from the /.is if key that could be combined with gernot's comment there is the /.is choice key handler. Here is yet another way which avoids the namespace problems and works with ifnum. Under the hood tikz works a bit like this, too.
documentclass[border=2mm, tikz]{standalone}
usepackage{tikz}
begin{document}
pgfkeys{/cis/.cd,show/.initial=1}

begin{tikzpicture}[]
coordinate[label=A](A) at (0,0);
coordinate[label=right:B](B) at (2,0);
coordinate[label=C](C) at (2,1);

ifnumnumexprpgfkeysvalueof{/cis/show}=1
draw[red, thick] (A) -- (B) -- (C) --cycle;
else% nothing
fi
end{tikzpicture}

begin{tikzpicture}[/cis/show=0]
coordinate[label=A](A) at (0,0);
coordinate[label=right:B](B) at (2,0);
coordinate[label=C](C) at (2,1);

ifnumnumexprpgfkeysvalueof{/cis/show}=1
draw[red, thick] (A) -- (B) -- (C) --cycle;
else% nothing
fi
end{tikzpicture}
end{document}

As for /.is if.
documentclass[border=2mm, tikz]{standalone}
usepackage{tikz}
begin{document}
newififcisshow
tikzset{cis/.cd,show/.is if=cisshow,show/.default=true,show=true}

begin{tikzpicture}[]
coordinate[label=A](A) at (0,0);
coordinate[label=right:B](B) at (2,0);
coordinate[label=C](C) at (2,1);

ifcisshow
draw[red, thick] (A) -- (B) -- (C) --cycle;
else% nothing
fi
end{tikzpicture}

begin{tikzpicture}[cis/show=false]
coordinate[label=A](A) at (0,0);
coordinate[label=right:B](B) at (2,0);
coordinate[label=C](C) at (2,1);

ifcisshow
draw[red, thick] (A) -- (B) -- (C) --cycle;
else% nothing
fi
end{tikzpicture}
end{document}

As mentioned already, /.is choice is another option, but this makes most sense if the options are not just Boolean.

TikZ: create a button to show something or not

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