Is it safe to turn off Pattern::patv?

Question

By default Mathematica throws a warning message if I use the same name for both Blank and BlankSequence patterns:

f[{x_, _         


        

Answer 1

When you switch the message off and afterwards on again, you write 3 lines to use your pattern. If you want to express that f should take the first element if it's given one list and take all elements if it's given more than one parameter, what's wrong with

f[{x_, ___}] := g[x];
f[x__] := g[x];

which is still one line less to write?

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But to give an opinion about your pattern: The problem I see here is

f[{x_, __} | x__] := {x};
g[x__ | {x_, __}] := {x};
f[{1, 2, 3}]
g[{1, 2, 3}]

Out[6]= {1}

Out[7]= {{1, 2, 3}}

This would be kind of unexpected and maybe hard to debug. Using two definitions with different patterns does the job right:

f[{x_, __}] := {x};
f[x__] := {x};
g[x__] := {x};
g[{x_, __}] := {x}
f[{1, 2, 3}]
g[{1, 2, 3}]

Out[7]= {1}

Out[8]= {1}