Re: [PATCH yew-widget-toolkit v3] widget: form: number: round floats to some decimal precision

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Am 05.05.26 um 15:25 schrieb Christoph Heiss:
> The decimal precision is controllable through a property.
> 
> E.g. previously, for an input like
> 
>   Number::new()
>       .name("some-float")
>       .step(0.1)
>       .value(0.2)
> 
> and pressing the "range-up" button on the input would result in
> 0.30000000000000004 - which is rather undesirable.
> 
> Rounding is done on step up, step down, on creation, on the validated
> form value and on the parsed value for `on_input`, if any.

While this should address such rounding on stepping, a user entering
0.30000000000000004 explicitly and then submitting that would still result
in the not-rounded value getting submitted.

What about just rounding in the validator, which is basically the single
source of truth and might also make this change a bit shorter. I.e., add
decimal_places to the ValidateClosure generic struct.

Am 05.05.26 um 15:25 schrieb Christoph Heiss:
> @@ -79,6 +81,12 @@ impl NumberTypeInfo for f64 {
>      fn is_decimal() -> bool {
>          true
>      }
> +    fn round_to_precision(&self, precision: u8) -> Self {
> +        // Do a little dance here to round to the nearest step value, by multiplying,
> +        // rounding to the nearest integer and dividing again
> +        let m = 10f64.powf(precision as f64);

As precision is always an integer this should probably use [powi] over
powf, which should be also slightly faster, not that it matters much here.

[powi]: https://doc.rust-lang.org/std/primitive.f64.html#method.powi

> +        (self * m).round() / m
> +    }
>  }
>  
>  // Note: Error message from rust parse() are not gettext translated, so try to do all