struct or class

FreeSlave via Digitalmars-d-learn digitalmars-d-learn at puremagic.com
Sun Aug 24 05:20:34 PDT 2014


On Sunday, 24 August 2014 at 11:56:44 UTC, nikki wrote:
> I come from languages that don't offer structs, I have this 
> json load function that has to keep some data and intuitively 
> I've written a struct, I've read about the differences, heap vs 
> stack, value vs reference, but know I think i am overthinking 
> it.
>
> Is this decent:
> 	bool loadFromFile (string path)
> 	{
> 		auto data = readText(path);
> 	        JSONValue parsed = parseJSON(data);
> 		
> 		struct AtlasSpriteData
> 		{
> 			SDL_Rect clipRectangle;
> 			int xOffset;
> 			int yOffset;
> 		}
> 		AtlasSpriteData[string] dict;
>
> 	        foreach( string name, value; parsed["frames"] ){
> 			SDL_Rect clipRectangle;
>                         auto spriteSourceSize = 
> value["spriteSourceSize"];
> 			clipRectangle.x = to!int(frame["x"].toString());
> 			clipRectangle.y = to!int(frame["y"].toString());
> 			clipRectangle.w = to!int(frame["w"].toString());
> 			clipRectangle.h = to!int(frame["h"].toString());
> 			int xOffset = to!int(spriteSourceSize["x"].toString());
> 			int yOffset = to!int(spriteSourceSize["y"].toString());
> 			auto data = AtlasSpriteData(clipRectangle, xOffset, yOffset);
> 			dict[name] = data;
> 		}
>
> Or should I use a class for that AtlasSpriteData?
> reading about it I get the impression everytime I'll look up 
> data from that dictionary data will get copied ?

Your struct instance will occupy only 24 bytes. It's ok even if 
you will copy it. I would avoid heap allocation in this case. 
Also what is 'frame' variable? I don't see local declaration of 
it. Or you just forgot to replace 'value' with 'frame'. Does not 
JSONValue.integer fit in this case instead of 
to!int(JSONValue.toString()) ?

Reading does not perform copy if you access struct directly as 
dict[name].some_field. Copying is performed only if you pass 
struct by value or assign it to variable.


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