bignum et.al and "constants"

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Moin,

I just noticed that when you do:

	perl -Mbignum -wle 'print 5'
	perl -Mbignum -wle 'print 5.1'

you end up with a Math::BigInt resp. Math::BigFloat "constant". However, 
these can be modified, and are sometimes, and sometimes not:

	# perl -Mbignum -wle 'for (0..2) { print 5->blog() }'
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526
	# perl -Mbignum -wle 'for (0..2) { print 5.1->blog() }'
	1.629240539730280087626788400111288032635
	0.4881139796953300666097741422180843672917
	-0.7172063354515893755243480929933879353687

The difference comes from the fact that in the first case, 
Math::BigFlow->blog() gets a Math::BigInt, makes a copy of that and returns 
the result. In the second case it actually modifies the passed-in value. 
Oops.

Now, technically you *should* write it like this (note "copy->"!):

	# perl -Mbignum -wle 'for (0..2) { print 5->copy->blog() }'
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526
	# perl -Mbignum -wle 'for (0..2) { print 5.1->copy->blog() }'
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526
	1.609437912434100374600759333226187639526

I think the right thing to do would be to catch modifications of constants, 
and warn. However, that would need Math::BigInt::Constant in the core, plus 
some tuits to make it actually work and not break anything else.

	# perl -Mbignum -MMath::BigInt::Constant  -wle 'for (0..2)\
	 { print Math::BigInt::Constant->new(5)->blog() }'
	Can not modify Math::BigInt::Constant 5 via blog()

Oh, and I just noticed Math::BigFloat::Constant doesn't even exist yet - 
although with all the hooks already in place, it would be trivial to set it 
up. Math::BigInt::Constant is about 1K of Perl code.

(But also maybe somebody else has a better (faster, less overhead) idea how 
to make Math::Big* objects constant.

All the best,

Tels
	
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• bignum et.al and "constants" by Tels