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John Carmack's comment on Doom 3's code style

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Re: John Carmack's comment on Doom 3's code style

#101

Post by Cushman »

jblow wrote: post #96
georgeorwell wrote: post #87

Earlier quoted context omitted.

It strikes me that your argument taken to the extreme is that everybody should program in assembly language because you can do anything, anytime, anywhere. Well, at least as far as control flow structures are concerned. Certainly C is preferable to C++ if you want simple and malleable code. Do you also prefer if-else to switch statements? (I'm not sure.) Do you like to use goto? (I doubt it.) Do you eschew the use of…

No, you clearly didn't understand my point. I am talking about maximizing the rate of successful features implemented. Programming things in assembly language is obviously not going to do that. I don't know, man. I have 31 years of programming experience. I am not detecting from your argument that you have anywhere near this level of experience, so I am inclined not to get into this discussion. But I will say that yo…

Not to repeat myself, but:

    if (a) 
      printf("returning b");
    return a ? b : c;
...makes it easy to modify the side effects of the return without muddying the semantics.

Re: John Carmack's comment on Doom 3's code style

#102

Post by to3m »

Cushman wrote: post #101
jblow wrote: post #96

Earlier quoted context omitted.

No, you clearly didn't understand my point. I am talking about maximizing the rate of successful features implemented. Programming things in assembly language is obviously not going to do that. I don't know, man. I have 31 years of programming experience. I am not detecting from your argument that you have anywhere near this level of experience, so I am inclined not to get into this discussion. But I will say that yo…

Not to repeat myself, but: if (a) printf("returning b"); return a ? b : c; ...makes it easy to modify the side effects of the return without muddying the semantics.

Now, let us suppose that expression a has side-effects...

"But that's just stupid!"

Yes. Now, given that a has side-effects...

Re: John Carmack's comment on Doom 3's code style

#103

Post by worldsayshi »

quux wrote: post #7
jlongster wrote: post #2

My heart grew a little warm with the last paragraph of John Carmack's comment: "The major evolution that is still going on for me is towards a more functional programming style, which involves unlearning a lot of old habits, and backing away from some OOP directions."

John Carmack wrote a nice article about experiences writing functional code in C++ here: http://www.altdevblogaday.com/2012/04/26/functional-programm...

"a function can still be pure even if it calls impure functions, as long as the side effects don’t escape the outer function"

This is a very good point that probably could be systematically exploited. Does anyone know examples of this?

Re: John Carmack's comment on Doom 3's code style

#104

Post by georgeorwell »

to3m wrote: post #99
georgeorwell wrote: post #87

Earlier quoted context omitted.

It strikes me that your argument taken to the extreme is that everybody should program in assembly language because you can do anything, anytime, anywhere. Well, at least as far as control flow structures are concerned. Certainly C is preferable to C++ if you want simple and malleable code. Do you also prefer if-else to switch statements? (I'm not sure.) Do you like to use goto? (I doubt it.) Do you eschew the use of…

Well, I might be unusual, but I don't object to goto, I don't uses classes and inheritance much - and I like code that's all in one file, too. (Means I can keep an eye on it.) So it might not surprise you to hear that I'd vote for the code that uses the if statement :) - in fact, I don't really understand why the second would ever be preferable, outside some unlikely case specially engineered to prove me wrong. I can…

All you need to do is hoist the conditionals out of the ?: if you have a bug and you want to inspect them, either with printf or a debugger. Everything else is available before the statement.

Personally I don't use debuggers except to get a backtrace from a core dump once in a while. I use various forms of automated testing and logging to stderr/stdout. They just aren't very useful with concurrency bugs.

Re: John Carmack's comment on Doom 3's code style

#105

Post by Cushman »

to3m wrote: post #102
Cushman wrote: post #101

Earlier quoted context omitted.

Not to repeat myself, but: if (a) printf("returning b"); return a ? b : c; ...makes it easy to modify the side effects of the return without muddying the semantics.

Now, let us suppose that expression a has side-effects... "But that's just stupid!" Yes. Now, given that a has side-effects...

Suppose I want to `printf("Returning. A: %i", a)`. Same answer.

Re: John Carmack's comment on Doom 3's code style

#106

Post by jblow »

dchichkov wrote: post #93
jblow wrote: post #82

Earlier quoted context omitted.

Not allowing other code in is a bad thing. See my putty reply above.

It depends. But in this particular case, some trivial extra code inserted inside that if statement may break things. Like breaking vectorization of that 'for' (note, that we are going over vertices). When you are writing the code, some times you may want to put additional constraints on the allowed operations, modifications, etc. A trivial example in C++ would be using 'const &' instead of '&'.

This is true (especially: breaking vectorization). But premature optimization is not a good idea, and if you are doing real optimization, you are going to rewrite that piece of code 10 times anyway, so it is in a different class of problem and the putty stuff I was saying before does not apply (i.e. this code is in the 1% or so of the codebase that is highly performance-sensitive).

Optimized code is just a different thing from general code (if one is a productive programmer).

Re: John Carmack's comment on Doom 3's code style

#107

Post by georgeorwell »

jblow wrote: post #96
georgeorwell wrote: post #87

Earlier quoted context omitted.

It strikes me that your argument taken to the extreme is that everybody should program in assembly language because you can do anything, anytime, anywhere. Well, at least as far as control flow structures are concerned. Certainly C is preferable to C++ if you want simple and malleable code. Do you also prefer if-else to switch statements? (I'm not sure.) Do you like to use goto? (I doubt it.) Do you eschew the use of…

No, you clearly didn't understand my point. I am talking about maximizing the rate of successful features implemented. Programming things in assembly language is obviously not going to do that. I don't know, man. I have 31 years of programming experience. I am not detecting from your argument that you have anywhere near this level of experience, so I am inclined not to get into this discussion. But I will say that yo…

I'm not even clear that it's clear I didn't understand your point. I guess I have trouble communicating effectively. I thought your point was that flexible control flow structures like if-else allow you to change code quickly and more easily in the future. Wasn't that the point?

Assuming I have understood your preference for flexible code, I am simply stating my belief that it is useful to balance this with rigid code. Sometimes the flexible code is simpler, easier to read and write, and more maintainable, sometimes the rigid code is simpler, easier to read and write, and more maintainable. It depends on what you are trying to do. In this particular case I prefer the ?:.

The assembly argument was based on a notion I had that any time you use something more complicated than test and branch for control flow you are introducing rigidity into your code. Often this lets you be productive too; switch statements are a good example.

And lastly, let's assume I am 14 years old. Is that really the way a wise teacher talks to the young and inexperienced? My favorite teachers ask questions to check and help deepen my understanding, and sometimes it's revealed that they're learning something too.

Re: John Carmack's comment on Doom 3's code style

#108

Post by fatbird »

jblow wrote: post #96
georgeorwell wrote: post #87

Earlier quoted context omitted.

It strikes me that your argument taken to the extreme is that everybody should program in assembly language because you can do anything, anytime, anywhere. Well, at least as far as control flow structures are concerned. Certainly C is preferable to C++ if you want simple and malleable code. Do you also prefer if-else to switch statements? (I'm not sure.) Do you like to use goto? (I doubt it.) Do you eschew the use of…

No, you clearly didn't understand my point. I am talking about maximizing the rate of successful features implemented. Programming things in assembly language is obviously not going to do that. I don't know, man. I have 31 years of programming experience. I am not detecting from your argument that you have anywhere near this level of experience, so I am inclined not to get into this discussion. But I will say that yo…

I have 31 years of programming experience. I am not detecting from your argument that you have anywhere near this level of experience, so I am inclined not to get into this discussion.

This is shitty.

Re: John Carmack's comment on Doom 3's code style

#109

Post by greiskul »

worldsayshi wrote: post #103
quux wrote: post #7

Earlier quoted context omitted.

John Carmack wrote a nice article about experiences writing functional code in C++ here: http://www.altdevblogaday.com/2012/04/26/functional-programm...

"a function can still be pure even if it calls impure functions, as long as the side effects don’t escape the outer function" This is a very good point that probably could be systematically exploited. Does anyone know examples of this?

I think caching/memoization is one of the most typical cases of this.

Re: John Carmack's comment on Doom 3's code style

#110

Post by georgeorwell »

to3m wrote: post #102
Cushman wrote: post #101

Earlier quoted context omitted.

Not to repeat myself, but: if (a) printf("returning b"); return a ? b : c; ...makes it easy to modify the side effects of the return without muddying the semantics.

Now, let us suppose that expression a has side-effects... "But that's just stupid!" Yes. Now, given that a has side-effects...

Assuming a has type int:

  int a_val = a;
  if (a_val)
    printf ("returning b");
  return a_val ? b : c;
Anyway, it's not useful for complicated code that needs to do lots of stuff. It's useful for simple code that ends up being more verbose with if-else. It's also useful for enforcing behaviour.
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