• frezik@midwest.social
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    7 months ago

    It’s only a const within a function. You can pass the value to another function and changing it as it’s passed. For example:

    const int foo = 1
    other_func( foo + 1)
    

    In functional programming, you tend to keep track of state on the stack like this.

      • frezik@midwest.social
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        7 months ago

        Keeping state managed. The data for the function will be very predictable. This is especially important when it comes to multithreading. You can’t have a race condition where two things update the same data when they never update it that way at all.

          • frezik@midwest.social
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            7 months ago

            Rather than me coming up with an elaborate and contrived example, I suggest giving a language like Elixir a try. It tends to force you into thinking in terms of immutability. Bit of a learning curve if you’re not used to it, but it just takes practice.

            • madcaesar@lemmy.world
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              7 months ago

              Ok how about this then, I frequently do something like this:

              let className = 'btn'
                if (displayType) {
                  className += ` ${displayType}`
                }
                if (size) {
                  className += ` ${size}`
                }
                if (bordered) {
                  className += ' border'
                }
                if (classNameProp) {
                  className += ` ${classNameProp}`
                }
              

              How would this be made better with a functional approach? And would be more legible, better in anyway?

              • frezik@midwest.social
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                7 months ago

                I’d say this example doesn’t fully show off what immutable data can do–it tends to help as things scale up to much larger code–but here’s how I might do it in JS.

                function generate_class_name( display_type, size, bordered, class_name_prop ) 
                {
                  classes = [
                      'btn',
                      ( display_type ? display_type : [] ),
                      ( size ? size : [] ),
                      ( bordered ? bordered : [] ),
                      ( class_name_prop ? class_name_prop : [] ),
                  ];
                
                  return classes.flat().join( " " );
                }
                
                console.log( "<"
                    + generate_class_name( "mobile", "big", null, null )
                    + ">" );
                console.log( "<"
                    + generate_class_name( "desktop", "small", "solid", "my-class" ) 
                    + ">" );
                console.log( "<"
                    + generate_class_name( null, "medium", null, null ) 
                    + ">" );
                

                Results:

                <btn mobile big>
                <btn desktop small solid my-class>
                <btn medium>
                

                Notice that JavaScript has a bit of the immutability idea built in here. The Array.flat() returns a new array with flattened elements. That means we can chain the call to Array.join( " " ). The classes array is never modified, and we could keep using it as it was. Unfortunately, JavaScript doesn’t always do that; push() and pop() modify the array in place.

                This particular example would show off its power a little more if there wasn’t that initial btn class always there. Then you would end up with a leading space in your example, but handling it as an array this way avoids the problem.

                • madcaesar@lemmy.world
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                  7 months ago

                  Very interesting. Actually the part you mention about there being an initial 'btn' class is a good point. Using arrays and joining would be nice for that. I wish more people would chime in. Because between our two examples, I think mine is more readable. But yours would probably scale better. I also wonder about the performance implications of creating arrays. But that might be negligible.