OpenEuphoria

Re: scope of variables

• Posted by jeremy (admin) Jan 01, 2011
• 2444 views

Declaring variables inside of the scope can make mainteance and readability much easier. It keeps variable definition close to variable use.

i.e.

function copy_file(sequence from_fname, sequence to_fname) 
    integer status 
 
    status = c_func(hCopyFile, { ... }) 
    if status = BAD then 
        sequence error_message = c_func(hErrMessage, { ... }) 
 
        log_error(error_message) 
 
        return { status, error_message } 
    end if 
 
    return status 
end function 

It can also prevent declaration when not necessary, i.e.

function backup_file(sequence fname) 
    sequence full_fname = absolute_filename(fname) 
 
    if not file_exists(full_fname) then 
        return { 0, "Source file not found" } 
    end if 
 
    sequence backup_fname = full_fname & ".bak" 
    if file_exists(backup_fname) then 
        return { 0, "Backup file already exists" } 
    end if 
 
    integer status = copy_file(full_fname, backup_fname) 
    if status = BAD then 
        sequence error_message = blah() 
        log_failure(error_message) 
        return { status, error_message, full_fname, backup_fname } 
    end if 
 
    return status 
end function 

Those are just two very simplistic examples. Declaring those at the top of the method declares variables that will not be used most of the time (a valid copy/backup). It also makes the point of definition futher from the point of use making it more difficult to follow when you begin to have hundreds of methods in your program. Code templates also can not be used as much if all variables are declared at the top of the procedure/function, reducing the automation gained by your editor/IDE and increasing potential for bugs. Declaring at the top instead of close to the use also encourages one to "reuse" a variable w/a slightly incorrect name. Another problem with declaring at the top is that the temp variable is not cleared until it goes out of scope, thus your program will use more memory (maybe not an issue for most routines but some it can be significant).

Much more complex examples of how declaring variables close to their use and w/in the blocks they are to be used can be found throughout the standard library, various 4.0 projects and various places in Euphoria code.

Jeremy