Crystal: Overflow in enum that has a negative value

[astellon]

I met compile error in enum that has a negative value.

The code:

enum Nums
  Zero  = -2
  One
  Two
end

The error:

Error in line 4: value of enum member Two would overflow the base type Int32

This error arises in 0.29.0, not 0.28.0. I know this is suppressed by specifying each value like:

enum Nums
  Zero  = -2
  One   = -1
  Two   = 0
end

This is a feature for safety or a bug of the compiler?

[straight-shoota]

Definitely a bug. Two should not be assigned a value that would overflow Int32.

[asterite]

The culprit is this line: https://github.com/crystal-lang/crystal/blob/e3fa96752588df94d386ce1551ad03526a8545c9/src/compiler/crystal/semantic/top_level_visitor.cr#L692

I wrote the overflow check incorrectly for negative values... I wish we had a way to try to do stuff and know whether it overflows without having to raise and catch an exception. Something like ?+ or Int32.add_with_overflow... that way I wouldn't have to do custom math to check things like this.

[wontruefree]

it would be nice to have has an api where you could get the result of the overflow. Something like unsafe_div except you would have to pass a pointer to the overflow var and check to see if it was set to 1 like it is here.

I was thinking something like.

overflow = 0
100.unsafe_mul(123, pointerof(overflow))

if overflow == 1
  p "* has overflowed"
end