Combining Items

ID:2086663
 
May 19 2016, 10:33 pm
(See the best response by Ter13.)
Code:
obj/scroll/recipe
    minor_hp_potion
        icon = 'Icons.dmi'
        icon_state = "Scroll1"
        var/materials
        verb
            Get()
                set src in oview(1)
                usr.contents += src
            Use()
                var/a = /obj/food/mushroom/red_mushroom
                var/b = /obj/alchemy/slime
                if(a && b in usr.contents)
                    new /obj/potion/hp/minor_hp_potion(usr.loc)


Problem description: Could someone show me what I did wrong and point me in the right direction? I have no errors or warnings, but the new item doesn't show up in game.

May 19 2016, 10:50 pm
Certainly at least one problem is this.
if(a && b in usr.contents)

This is parsed as
if(a && (b in usr.contents))

The second is that neither of those typepaths will be in usr.contents, even though items of that time may be.
May 19 2016, 10:51 pm
Best response
Let's talk generics. You are going to want to minimize the amount of work you need to do for each recipe by using generic behavior.

obj/item
    var
        usable = 0
    verb
        Get()
            set src in oview(1)
            if(isturf(loc))
                loc = usr

        Drop()
            set src in usr
            if(loc==usr)
                loc = usr.loc

        Use()
            set src in usr
    New()
        if(!usable) verbs -= /obj/item/verb/Use
        ..()


You don't want to redefine the get/drop business for every single item. Just define it on a root type like /obj/item.

Now let's create a crafting recipe with the generic behavior out of the way:
obj/item/scroll/recipe
    usable = 1
    var
        list/ingredients
        creates
    proc
         Craft(mob/m)
             var/list/inv = m.contents.Copy()
             var/list/found = list()
             var/obj/item
             for(var/t in ingredients)
                 item = locate(t) in inv
                 if(item)
                     inv -= item
                     found += item
                 else
                     return null
             for(var/obj/i in inv)
                 del i
             return new creates()
    Use()
        set src in usr
        if(loc==usr)
            var/obj/item/i = Craft(usr)
            if(i) i.loc = usr


Now let's set up a recipe:

obj/item/scroll/recipe
    minor_hp_potion
        ingredients = list(/obj/item/food/mushroom/red_mushroom,/obj/item/alchemy/slime)
        creates = /obj/item/potion/hp/minor_hp_potion


And there you have it. No need to rewrite your code for every possible recipe. Set it up once and forget about it.
May 20 2016, 5:12 am
It's probably also important to note that the |= operator allows you to add something to a list only if it isn't already in the list, even though it's only a safety check and isn't typically necessary.

e.g.
mob/verb/joinGroup()
  usr.group |= src
May 20 2016, 9:07 am
Of course there is a downside to defining recipes in this way: the ingredients list is initialized at runtime, in a hidden init proc. If a lot of these run when your world begins, it can slow things down. But it's a pretty simple way to get it setup.

Another option you have with crafting is using associative lists. If you want to use 2 of an item, rather than adding it twice to the list you could set /obj/item/blah=2 and then modify your crafting like so:

    proc
         Craft(mob/m)
             var/list/inv = m.contents.Copy()
             var/list/found = list()
             var/obj/item
             for(var/t in ingredients)
                 var/quantity = ingredients[t] || 1
                 while(quantity-- > 0)
                     item = locate(t) in inv
                     if(item)
                         inv -= item
                         found += item
                     else
                         return null
             for(item in inv)
                 del item
             return new creates()

Of course crafting can be as complex as you like: creating multiple items in a single reaction, adding catalysts, factoring in chances for failure and other items you might get as a result, etc.

If your game gets very big, you may want to get away from hard-coding things and instead move toward putting your recipes, and even many of your items, in a file that you can read as needed.