print scalar (1,2,3,4)[2];
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Doesn't work, because you seem to want the scalar value of an array (it's size), but you're specifying a list.

I think that you are wrong on this one, notice:

print scalar (1,2,3,4)[2];    # syntax error at )[
print scalar((1,2,3,4)[2] );  # prints 3
print scalar+(1,2,3,4)[2];    # also prints 3
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Your first answer applies to both. The scalar is just hogging the parens. It is also useless, as it is forcing a scalar context on a scalar.