Issue 4120 added an implicit cast for BigInt to a boolean value.

This used to work:

/// Returns a mutable copy of a BigInt
public BigInt mutable(const BigInt num)
{
	BigInt big = cast(BigInt)num;
	return big;
}

But it now generates an error:

Error: template instance opCast!(BigInt) does not match template declaration opCast(T : bool)()

Is there another way to make a mutable copy of a BigInt?

Paul D. Anderson:

> Is there another way to make a mutable copy of a BigInt?

For now don't make bigints constant. const=>mutable cast is not a good idea in general, in D.

Bye,
bearophile

On Thursday, 30 May 2013 at 22:57:20 UTC, bearophile wrote:
> Paul D. Anderson:
>
>> Is there another way to make a mutable copy of a BigInt?
>
> For now don't make bigints constant. const=>mutable cast is not a good idea in general, in D.
>
> Bye,
> bearophile

It's like the old joke: "Doc, it hurts when I do this." Doctor: "Don't do that!"

I need both constant and mutable BigInts.

I don't want to convert a constant value to mutable, I just want a mutable copy. The cast was just a way to make a mutable copy but it's broken now.

Other types have a .dup property which returns a mutable copy, but BigInt doesn't.

Paul

On Thursday, 30 May 2013 at 22:32:08 UTC, Paul D. Anderson wrote:
> Issue 4120 added an implicit cast for BigInt to a boolean value.
>
> This used to work:
>
> /// Returns a mutable copy of a BigInt
> public BigInt mutable(const BigInt num)
> {
> 	BigInt big = cast(BigInt)num;
> 	return big;
> }
>
> But it now generates an error:
>
> Error: template instance opCast!(BigInt) does not match template declaration opCast(T : bool)()
>
> Is there another way to make a mutable copy of a BigInt?

This doesn't work either, by the way:

    BigInt big = BigInt(num);

Error: template std.bigint.BigInt._ctor does not match any function template declaration. Candidates are:
... std.bigint.BigInt.__ctor(T : const(char)[](T s)
... std.bigint.BigInt.__ctor(T x) if (isIntegral!(T))

Paul D. Anderson:

> It's like the old joke: "Doc, it hurts when I do this." Doctor: "Don't do that!"

And it's a good advice because:
- The mammalian body is able to heal a surprisingly high number of problems by itself, given the right conditions and enough time. In such time avoiding to do "that" (like jumping on a knee that hurts) is a good advice, and it's often one of the conditions for the healing.
- Even if the body needs a bit of help from medicine, avoiding hurting a sore spot is often a good idea. Especially when there is no good cure available (like in many orthopaedic problems, that have surgery solutions that often cause more problems than the original problem).


> I need both constant and mutable BigInts.

Me too. In the last years I've put some bug reports on this in Bugzilla. Don is well aware that bigints are not const-corrected. It's a matter of working on them and fixing the problem, because maybe now D has all the tools to perform this fix/improvement.

In the meantime my advice is to not use const bigints.

Bye,
bearophile