Background

In the course of software application development, a good engineer will have a read of errors that can be encoutered when the application is ran.

Lineage

1. Software Development:- Function Declaration – Exceptions – Java
   Link
2. Software Development:- Function Declaration – Exceptions – Rust
   Link

Code

Outline

1. Import
   • std::error::Error
2. Constants
   • const emptyString:&str = “”;
   • const isKJV_false:bool = false;
3. Declare Variables
   • structures
     • Congregant
       • personName:String
       • bibleTranslation:String
       • isKJV:bool
       • err:String
4. Functions
   • listView
     • Arguments
       • list_of_Congregant:Vec<Congregant>
     • Steps
       • Iterate List
         • for (i, x) in list_of_Congregant.iter().enumerate()
   • listEvaluate
     • Arguments
       • list_of_Congregant:&mut Vec<Congregant>
     • Steps
       • Iterate List
         • for x in list_of_Congregant.iter_mut()
           • As list will be modified replaced iter with iter_mut
         • reset contextual variables
           • errLocal
             • errLocal = “”.to_string();
         • Make copy of contextual data
           • bibleTranslation
             • bibleTranslationLocal = x.bibleTranlation.to_owned();
         • Invoke Function ( bibleIsKJV )
           • isKJV_context = bibleIsKJV(bibleTranslationLocal);
         • Review Function Return Value ( isKJV_context )
           • is_ok()
             • If isKJV_context.is_OK
               • Unwrap Result
                 • isKJV = isKJV_context.unwrap();
           • is_err()
             • If isKJV_context.is_err()
               • Unwrap Error
                 • let err = isKJV_context.unwrap_err();
               • save errorLocal
                 • errLocal = err.to_string()
   • bibleIsKJV
     • Function Declaration
       • fn bibleIsKJV ( bibleTranslation:String ) -> Result<bool, Box<dyn Error>>
     •  Arguments
       • bibleTranslation:String
     • Return
       • Result<bool, Box<dyn Error>>
     • Steps
       • if bibleTranslation != “KJV”
         • Format Error Message

           •  errorMessage = format! ( "Bible is not KJV. It is '{0}'" , bibleTranslation ); 

         • Raise Exception

           •  return Err ( errorMessage.into() ); 

5. Main Function
   • Declare Variables
     • declare list
       • let mut list_of_Congregant: Vec<Congregant>;
     • declare local variables
       • let mut personName:String;
         let mut bibleTranslation:String;
         let mut emptyStringLocal:String;
   • Initialize Variables
     • Initialize empty vector
       • list_of_Congregant = vec![];
   • Create structures
     • Set Local Variables

       // Create struct with field init shorthand
       personName = String::from("Peter Johnson");
       bibleTranslation = String::from("KJV");
       emptyStringLocal = emptyString.to_owned();

     • Initialize structure

       let peterJohnson = Congregant
       {
             personName: personName
           , bibleTranslation : bibleTranslation
           , isKJV : isKJV_false
           , err: emptyStringLocal
       };
       

 

Code Snippet

/*
    Import Traits
*/
use std::error::Error;

/*
    Declare Constants
*/
const emptyString:&str = "";
const isKJV_false:bool = false;
    
/*
    Declare structure Congregant
*/

#[derive(Debug)]
struct Congregant 
{
      personName: String
      
    , bibleTranslation: String
    
    , isKJV: bool
    
    , err:String
    
}

/*
    listView
*/
fn listView(list_of_Congregant:Vec<Congregant>)
{
   
    for (i, x) in list_of_Congregant.iter().enumerate() 
    {
    
          println!
          (
              "{:0?}) {:0?}"
            , i
            , x
          );
          
          println!("");
          
    }
    
}

/*
    listEvaluate
*/
fn listEvaluate
(
    list_of_Congregant:&mut Vec<Congregant>
)
{
  
    /*
        Declare function return variable
    */
    let mut isKJV_context:Result<bool, Box<dyn Error>>;
    
    let mut isKJV:bool = false;
    
    let mut bibleTranslationLocal:String;
    
    let mut errLocal:String;
    
    /*
        Iterate list
            Mutatable List
                iter() versus iter_mut() 
    */
    for x in list_of_Congregant.iter_mut() 
    {
    
        //reset context variables
        
             //set local error
            errLocal = "".to_string();
        
        //get a copy of bible name
        bibleTranslationLocal = x.bibleTranslation.to_owned();
        
        // determine if bible is KJV?
        isKJV_context = bibleIsKJV(bibleTranslationLocal);
        
        
        /*
            If return variable is OK, then it is usable
        */
        if isKJV_context.is_ok()
        {
      
           // Consume the result and return the contents with `unwrap`.
           isKJV = isKJV_context.unwrap();
           
        }      

        else if isKJV_context.is_err()
        {

          isKJV = false;

          //unwrap Error
          let err = isKJV_context.unwrap_err();
          
          //save errorLocal
          errLocal = err.to_string()
          
        }
        
        //save test
        x.isKJV = isKJV;
        
        //save exception
        x.err = errLocal;
        
        
          
    } //for 
    
}


fn bibleIsKJV
(
     bibleTranslation:String
) -> Result<bool, Box<dyn Error>>
{

    let errorMessage:String;
    
    /*
        If bible name is not KJV, raise exception
    */
    if bibleTranslation != "KJV"
    {
      
      errorMessage = format!
                        (
                              "Bible is not KJV.  It is '{0}'"
                            , bibleTranslation
                        );
                        
      //raise informative error
      //convert string to err type
       return Err
            (
                errorMessage.into()
            );
            
    }
    
    //return OK and true (as result)
    return Ok(true);
    
}

fn main() 
{
   
    //declare list
    let mut list_of_Congregant: Vec<Congregant>;
    
    let mut personName:String;
    let mut bibleTranslation:String;
    let mut emptyStringLocal:String;
       
    //initialize empty vector
    list_of_Congregant = vec![];
    
    // Create struct with field init shorthand
    personName = String::from("Peter Johnson");
    bibleTranslation = String::from("KJV");
    emptyStringLocal = emptyString.to_owned();

    //Initialize structure
    let peterJohnson = Congregant 
                            { 
                                  personName: personName
                                , bibleTranslation : bibleTranslation
                                , isKJV : isKJV_false
                                , err: emptyStringLocal 
                            };
                           
    //Add structure to list 
    list_of_Congregant.push(peterJohnson);
    
    // Create struct with field init shorthand
    personName = String::from("Sylvia Brown");
    bibleTranslation = String::from("The Passion Translation");
    emptyStringLocal = emptyString.to_owned();
    
    //Initialize structure    
    let sylviaBrown = Congregant
                      { 
                              personName: personName
                            , bibleTranslation : bibleTranslation
                            , isKJV : isKJV_false
                            , err: emptyStringLocal
                      };
                          
    //Add structure to list                             
    list_of_Congregant.push(sylviaBrown);
    
       // Create struct with field init shorthand
    personName = String::from("Paul Young");
    bibleTranslation = String::from("NIV");
    emptyStringLocal = emptyString.to_owned();
    
    //Initialize structure    
    let paulYoung = Congregant
                    { 
                          personName: personName
                        , bibleTranslation : bibleTranslation
                        , isKJV : isKJV_false
                        , err: emptyStringLocal
                    };
                          
    //Add structure to list                             
    list_of_Congregant.push(paulYoung);
    
    //evaluate list of congregants
    listEvaluate
    (
        &mut list_of_Congregant
    );
    
    //list congregants
    listView
    (
        list_of_Congregant
    );
    
    
    
}

Output

OnlineGDB

Image

Textual

In position 0 we have value Congregant { name: "Peter Johnson", bible: "KJV", isKJV: true, err: "" }
In position 1 we have value Congregant { name: "Sylvia Brown", bible: "Passion Edition", isKJV: false, err: "Bible is not KJV. It is 'Passion Edition'" }

Online Code IDE

OnlineGDB

1. RustKJVOnly
   Link

Source Code Control

GitLab

1. Rust – Exception Handling
   • Link
     Link
   • Files
     • 01) RustKJVOnly.rs

Summary

In this post, reviewed the data returned from our function.

1. Returned Value
   • if is_ok()
     • unwrap function
       • retrieved returned value via the unwrap function
   • if is_err()
     • unwrap_err function
       • retrieved error value via the unwrap_err function