From: arne@vajhoej.dk   
      
   On 11/18/2025 2:04 PM, Arne Vajhøj wrote:   
   > On 11/15/2025 9:16 PM, Dan Cross wrote:   
   >>> Also note the availability of the 'Valid attribute to make sure that   
   >>> what   
   >>> is in the variable after the unsafe conversion is actually a valid   
   >>> value.   
   >>   
   >> Sum types make this trivial:   
   >>   
   >>      impl SomeType {   
   >>          fn try_from(i: i32) -> Option {   
   >>              // if valid, return `Some(whatever`),   
   >>              // else return `None`.   
   >>          }   
   >>      }   
   > (assuming Option in Rust is what it is in other languages)   
   >   
   > Option and Ada Valid are somewhat different.   
   >   
   > Option is a way for a function/method to either return   
   > a value or return the fact that there is no value.   
   >   
   > A much better way to do that than traditional   
   > return null or -1 or whatever to indicate there   
   > is no value.   
   >   
   > Ada valid attribute is a runtime check on the result from   
   > an unsafe conversion to see if it meets the constraints   
   > of the data type.   
      
   Option is in fashion in recent years.   
      
   There are not that many languages on VMS supporting   
   Option.   
      
   Scala does - Option[T].   
      
   And Java 8 Optional is almost the same.   
      
   Arne   
      
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