0, 0e0, 0.0, -0, +0, 000 all mean the same thing to Perl, why?

Just puzzling to me.

Related, but di开发者_运维知识库fferent question: What does “0 but true” mean in Perl?

Perl doesn't distinguish kinds of numbers. Looking at all of those with a non-CS/programmer eye, they all mean the same thing to me as well: zero. (This is one of the foundations of Perl: it tries to work like people, not like computers. "If it looks like a duck....")

So, if you use them as numbers, they're all the same thing. If you use them as strings, they differ. This does lead to situations where you may need to force one interpretation ("0 but true"; see also "nancy typing"). but by and large it "does the right thing" automatically.

I don't understand, what else should they mean?

You give integer, scientific, floating point, signed integers and octal notations of zero. Why should they differ?

0==0 as everyone, including Larry Wall, knows.

Perl interprets every scalar value as both a string and (potentially) a number. All of those string representations of zero can convert to the integer value 0 , according to perl's conversion rules:

"0", "0.0", "-0", "+0", "000" => Simplest case of straight string to numeric conversion. "0e0" => In a numeric context, only the leading valid numeric characters are converted, so only the leading "0" is used. For example, "1984abcdef2112" would be interpreted numerically as 1984.

"0 but true" in perl means that a string like "0e0" will evalutate numerically to 0, but in a boolean context will be "true" because the conversion to boolean follows different rules than the strict numeric conversion.

Perl works in contexts. In string context, they are all different. In numeric context, they are all zero.

print "same string\n" if '0' eq '0.0';
print "same number\n" if 0 == 0.0;

'0 but true' in boolean context is true:

print "boolean context\n" if '0 but true';
print "string context\n" if '0 but true' eq '0';
print "numeric context\n" if '0 but true' == 0;