all: support map[f32]string and map[f64]string (float map keys) too #8556
Conversation
|
perhaps change the message of line 83 of |
| @@ -2471,7 +2471,7 @@ fn (mut g Gen) map_fn_ptrs(key_typ table.TypeSymbol) (string, string, string, st | |||
| key_eq_fn = '&map_eq_int_2' | |||
| clone_fn = '&map_clone_int_2' | |||
| } | |||
| .int, .u32, .rune { | |||
| .int, .u32, .rune, .f32 { | |||
| hash_fn = '&map_hash_int_4' | |||
| key_eq_fn = '&map_eq_int_4' | |||
There was a problem hiding this comment.
Floats were deliberately left out (for the non-string keys work) because they can have different bit patterns which still compare as equal with ==. So it should use a different equality function. The hash function probably needs to be specific to floats too.
There was a problem hiding this comment.
Because of the +-0 and the nans?
There was a problem hiding this comment.
I'll add custom hash functions, I have not thought about them, thanks.
There was a problem hiding this comment.
I think this should work fine? However, it is a bit weird to use floats as keys in a map. Not sure when you would ever want to do that.
There was a problem hiding this comment.
I intend to port this: https://hg.python.org/cpython/file/1eee26b74e4b/Python/pyhash.c#l86 @ntrel .
There was a problem hiding this comment.
@ka-weihe it was weird to me too (I've never used floats for keys in a hash map before), but it was asked for by @shadowninja55 in the discord channel, it was easy to do, and is consistent with the rest of the language, so I think it will be a good addition.
There was a problem hiding this comment.
yeah honestly i probably wouldn't use it much either, but it's always good to support everything we can.
There was a problem hiding this comment.
If Kaspar thinks it's fine, I expect it is.
There was a problem hiding this comment.
Well, it is probably not going to behave like some people would expect it to... Only floats with the exact same bits will match.
|
Honestly, using floats as map keys just sounds wrong. Floats are notoriously hard to compare, and what's the use case? I'd be in favor of not allowing float keys. |
|
I use them for caching common pre-calculated values on a timeline in my current game. Float keys have their usage in the real world - although it's surely less common as mentioned. They can be good for caching certain value ranges or lookups where you know how to cut the decimals cutting overhead for string conversions. |
|
ok, sounds useful |
|
Yes, having float keys in maps is useful. Thanks for supporting this! But unfortunately currently float comparisons are undefined in V and from there follows, that withdrawal of values from such a map is also undefined. It's maybe time to finally tackle this... |
With this PR:
works.