what is the difference

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Rakiayn
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what is the difference

Post by Rakiayn »

between

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If ((other.isa('something'))
{
...
}
and

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if (something(other) != none)
{

}
Darkness
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Re: what is the difference

Post by Darkness »

I believe something(other) might return accessed nones.

Usually you do a check with .IsA, and then, if you wanna run specific functions on it, you may name it locally. Example:

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function something()
{
	local pawn p;

	if ( owner != none && owner.IsA('Pawn') ) // check if it's a pawn, since owner can be any actor
	{
		p = pawn(owner);
		p.health = 100;
		p.groundspeed = 500;
		...
	}
}
At least that's how I use them, based on observation. If I do something like pawn(owner).health = 100, without checking if only owners that are pawn, it would return an accessed none, in case it wasn't a pawn.

But of course you could use pawn(owner).health = 100 if it's a place where you ALWAYS know that:
a - there would ALWAYS be an owner;
b - owner would ALWAYS be a pawn.

I also tend to name things locally, even if I know there'll always be a specific type to run the function, to make it shorter and more organized, but usually it's only worth when you're going to use plenty lines with the same actor, in his more specific class (e.g playerpawn).
Last edited by Darkness on Mon Mar 08, 2010 8:32 pm, edited 2 times in total.
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Shadow
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Re: what is the difference

Post by Shadow »

The first one checks if an entity of that class with that class name exists (also affecting referenced subclasses)

The second is a (meta)typecast from a parent class to a subclass, if the entity/reference of the parent class is known, it returns the cast type, though one does not always know if that reference to the entity exists one first checks with the NOT (!=) operator that there's no NULL reference, which would lead to the infamous accessed nones.
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Feralidragon
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Re: what is the difference

Post by Feralidragon »

Also:

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other.isa('something')
Works between different packages, without the need of compile them all or add them to the EditPackages list.

While:

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something(other)
Only works if the Class something exists in your package or in another package above in EditPackages.

So depending on the situation, it might be better to use one or another, since the first is independent but is suitable to typing errors which will compile correctly, but the code might not work in the game and then you take ages just to find you mistyped the class name, and the second is dependent from a really existing class in your package or another package, and it won't work if it doesn't exists, but if you mistype it, it will stop the compilation and give an error there, and you will be able to correct it right away.
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Rakiayn
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Re: what is the difference

Post by Rakiayn »

ok thanx!
I usually use the second . but I think I will use the first one more often. being able to refer to ther packages with the game really needing to have it is a very nice
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Barbie
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Re: what is the difference

Post by Barbie »

Old thread but still facts in fog:
Do

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SomeActor.IsA('WhatEverClass')
results in the same as

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String(SomeActor.Class.name) ~= "WhatEverClass"
?
While on the other hand such as

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SomeActor(OtherActor) != None
ClassIsChildOf(class TestClass, class ParentClass)
do a binary compare in the object tree?
"Multiple exclamation marks," he went on, shaking his head, "are a sure sign of a diseased mind." --Terry Pratchett
Buggie
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Re: what is the difference

Post by Buggie »

1. No. It check all parents names too. Not just this class name.
2. "SomeActor" will be expanded by linker on compile time.
Same with classes send as params to ClassIsChildOf.
So there you operate were specific classes and similar names not work.
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sektor2111
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Re: what is the difference

Post by sektor2111 »

My two cents around - looking at post from 2010

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if (....Owner.Isa('Pawn'))
it's more like wreck and it slows down all time - you can use a Bool first, before testing what sort of pawn is that or else you'll test everything if it's desired Pawn.

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if (....Owner.bIsPawn) //Prevent Non-Pawns from being checked and it takes almost nothing in CPU timer
{
	//Do the rest of checks
}
Last time when I did some clocking execution on my rig it took 0.000000 seconds to check a boolean while ISA was longer.

As for ISA('Pawn') and Pawn(Other) != None I got the same results because I USED Both cases - ISA to me was a tiny bit slower...

UnType.h

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//
// See if this object belongs to the specified class.
//
inline UBOOL UObject::IsA( class UClass* SomeBase ) const
{
	guardSlow(UObject::IsA);
	for( UClass* TempClass=Class; TempClass; TempClass=(UClass*)TempClass->SuperField )
		if( TempClass==SomeBase )
			return 1;
	return SomeBase==NULL;
	unguardobjSlow;
}
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Re: what is the difference

Post by Buggie »

this is c++. So by code you never know what happen here because each operator can be overloaded with any fancy stuff.
In general, I have to admit that I’m a little bit scared of language features that hide things. When you see the code

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    i = j * 5;
… in C you know, at least, that j is being multiplied by five and the results stored in i.

But if you see that same snippet of code in C++, you don’t know anything. Nothing. The only way to know what’s really happening in C++ is to find out what types i and j are, something which might be declared somewhere altogether else. That’s because j might be of a type that has operator* overloaded and it does something terribly witty when you try to multiply it. And i might be of a type that has operator= overloaded, and the types might not be compatible so an automatic type coercion function might end up being called. And the only way to find out is not only to check the type of the variables, but to find the code that implements that type, and God help you if there’s inheritance somewhere, because now you have to traipse all the way up the class hierarchy all by yourself trying to find where that code really is, and if there’s polymorphism somewhere, you’re really in trouble because it’s not enough to know what type i and j are declared, you have to know what type they are right now, which might involve inspecting an arbitrary amount of code and you can never really be sure if you’ve looked everywhere thanks to the halting problem (phew!).

When you see i=j*5 in C++ you are really on your own, bubby, and that, in my mind, reduces the ability to detect possible problems just by looking at code.

None of this was supposed to matter, of course. When you do clever-schoolboy things like override operator*, this is meant to be to help you provide a nice waterproof abstraction. Golly, j is a Unicode String type, and multiplying a Unicode String by an integer is obviously a good abstraction for converting Traditional Chinese to Standard Chinese, right?
https://www.joelonsoftware.com/2005/05/ ... ook-wrong/

In this concrete code:

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if( TempClass==SomeBase )
You not know what happen here. Look like operator overloaded and classes equals when has same names. Possible exists another checks. IDK.

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TempClass=(UClass*)TempClass->SuperField
What about this? This too all transparent?
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