flatMap

Allows safely extracting a value expressed as a path containing optional or try values.

Using flatMap allows concise and safe expressions avoiding the need to check if optional or try values have valid values. Usage is not limited to optional and try type fields. Mandatory fields can also be traversed using flatMap.

Given the definition below:

record RecA {
   A : int
}

record RecB {
   B : try< RecA >
}

record RecC {
   C : RecB?

   assert IsValid {
      let optA : int? = flatMap( C.B.A )
   }
}

Observe the use of flatMap( C.B.A ). flatMap allows traversing optional and try objects to access a nested field. If there is no value present in the optional or try type field at any point in the nested access, flatMap returns none. For example if C contained a none value or if B contained a failure value, a none value is returned.

Without flatmap, C.B.A is an invalid expression as C.B is an invalid expression given C is an optional value.

Parameters:

No.	Type	Comments
1	Any field, variable	Path to a nested field

Returns: T? - If the target field type is T ?, the same type will be returned. If target is T ( not optional ), T ? will be returned.

Usages:

• flatMap( Field1.NestedField1.NestedField2 ) : T ?

Example:

Using flatMap to access value deeply nested within optional fields.

assert ValidDates {
    let effective = flatMap( EffectiveDate.UnadjustedDate.Value )
    let termination = flatMap( TerminationDate.UnadjustedDate.Value )

    return if ( !isNone(effective) && !isNone(termination) && get( effective ) > get( termination ) )
               some("Effective date ${effective} greater than Termination date ${termination}")
           else
               none
}