How to copy a struct ?

[DaveInDev]

Hi,

I have an array of structs called tab (all have the same variables), and let say that I would like to insert in position 5 a copy of the struct in position 3.

If I just make array_insert(tab,5,tab[3]), it will only copy a reference or the id of the struct in position 3.
So if I modify tab[5] content, I will also modify tab[3] content...

Thats' not what I want, I need to clone the struct in tab[3] to create a brand new object.
How can I do this ? I do not find any builtin function, nor any answer if I type "GMS2 copy struct" in google...

Am I supposed to create mu own deepcopy function that would recursively copy my struct ? (BTW, did I mention that my struct contains arrays and other structs ?... )

 

[Greenblizzard]

If you know the kind of data the struct contains, and they all have constructors, I'd recommend just writing it and all contained structs a Copy() method that spits out a clone of itself and its contained data, recursively calling Copy() on eventual struct members. This would surely run faster than anything scanning for variables and datatypes. Or you could use a pre-made library such as SNAP by JujuAdams https://github.com/JujuAdams/SNAP

 

[Pixel-Team]

You can use variable_struct_get() and variable_struct_set() to make a copy of an existing struct and its variables at runtime.

 

[DaveInDev]

Ok, thanks, just wanted to know if I missed something in the builtin functions. So i'll program my own recursive deep copy.

 

[31Nf4ChZ4H73N]

I use this function to copy a struct:

function copyStruct(struct){
    var key, value;
    var newCopy = {};
    var keys = variable_struct_get_names(struct);
    for (var i = array_length(keys)-1; i >= 0; --i) {
            key = keys[i];
            value = struct[$ key];
            variable_struct_get(struct, key);
            variable_struct_set(newCopy, key, value)
    }
    return newCopy;
}

 

[WangleLine]

I use this function to copy a struct:

function copyStruct(struct){
    var key, value;
    var newCopy = {};
    var keys = variable_struct_get_names(struct);
    for (var i = array_length(keys)-1; i >= 0; --i) {
            key = keys[i];
            value = struct[$ key];
            variable_struct_get(struct, key);
            variable_struct_set(newCopy, key, value)
    }
    return newCopy;
}

Sadly this doesn't quite work if you have nested structs (structs inside structs), as any included struct will only be copied by reference

 

[Zhanghua]

When do we have "struct_map" "struct_for_each" etc.?
rwkay


I burst my DeepClone function from 350ms to 200ms per 10000 times.
Share it with guys~~

function DeepCloneArray(s){
  return array_map(s,function(e){
       if( is_array(e) ){ return DeepCloneArray(e); }
       else if( is_struct(e) ){ return DeepCloneStruct(e); }
       return e;
  });
}

function DeepCloneStruct(s){
    return array_map(
        variable_struct_get_names(s),
        method({ctx: s},function(nm){
            var e = ctx[$ nm];
            if( is_array(e) ){ return DeepCloneArray(e); }
            else if( is_struct(e) ){ return DeepCloneStruct(e); }
            return e;
        })
    );
}

function DeepClone(s){
    if( is_array(s) ){ return DeepCloneArray(s);}
    else if( is_struct(s) ){ return DeepCloneStruct(s);}
    return s;
}

 

[chirpy]

@Zhanghua
Good code, but what is array_map? Is it a beta gml function?
Also, this doesn't seem to handle cyclic structs like builtin string(_struct) does.

var hello = { hello:"world" };
var world = { oops: hello };
hello.world = world;

//var ouch = DeepClone(hello);
var ouch = hello;
show_debug_message(string(ouch));

 

[sixonekevin]

It feels crunchy and might have issues depending on your data types but tbh I think the easiest way is just to stringify and then parse it.

 

[Zhanghua]

beta function.
cycle reference should be avoid by yourself considering the efficiency.
If you want to make a graph struct, you should craft anothor graph copy function.

 

[ricardo1996]

Here's a lil function I made.

/// @function struct_update(source, target, replace)
/// @description Copy/Replace keys from source struct to target struct. Note data structures will not be deep copied.
/// @param {Struct} source Source struct to copy from.
/// @param {Struct} target Target struct to copy to.
/// @param {Bool} replace Overwrite existing target keys with source keys.
function struct_update(s, t, r = false)
{
    for(var i = 0, a = variable_struct_get_names(s), l = array_length(a); i < l; ++i)
    {
        var
        k = a[@ i],
        v = s[$ k],
        c = t[$ k];
        if(c != undefined)
        {
            if(is_array(v))
            {
                var u = array_length(c);
                for(var o = 0, p = array_length(v); o < p; ++o)
                {
                    if(!r && o < u) continue;
                    c[@ o] = v[@ o];
                }
                continue;
            }else if(is_struct(v))
            {
                struct_update(v, c, r);
                v = c;
            }else if(!r) continue;
        }
        t[$ k] = v;
    }
}

data structures aren't deep copied

 

[FlowSwitch]

For anyone looking for answer to this question, like I was, about a year ago Gamemaker added a new function "variable_clone()" which will copy arrays, structs etc. down over 100 layers.