Possible history table improvement

[AlvaroBegue]

Now I'm very careful with C operators. Mistying a '&&' into a '&', or making wrong assumptions about operator precednece and default associativity, has cost me quite a few hours of debugging already.

I use & and | in stead of && and || quite often. This can save you branches, and branches that are not there can also not be mispredicted.

Hmmm... I would rather make the intent obvious by using && and || for booleans and & and | for bitwise operations, and let the compiler figure out how to save the branch, if it is a good idea. Compilers are pretty smart these days.

[lucasart]

And when I wrote that I thought that & had a higher priority than <.
That was also wrong. We learn: Just use a lot of () and be careful with & in conditions.

The C operator precedence table is way too big and complex to fit in my brain. I never try to learn and remember it, but accept that I do not want to remember it. If I did learn it off by heart, I would be too tempted to write obscure code, by abusing my knowledge of it, which is not a good thing.

I only remember the stuff that I use most often, and the rest (un-obvious) I prefer to use () to (i) be sure it works (ii) make the code more self-obvious.

But sometimes I read other people's code, and some people love to abuse their knowledge of C operator precedence to write obscure code. So I just Google for "C operator precedence".

For example, I've noticed that Marco likes to use the right-to-left associativity of the ternary operator '? :' to chain conditions (and save lines of code) like this:

Code: Select all

a = b ? c : d ? e : f;

which is equivalent to

Code: Select all

a = b ? c : (d ? e : f);

I learnt this 'trick' reading stockfish, but I prefer not writing code like that, as it takes too much brain power to read.

[AlvaroBegue]

For example, I've noticed that Marco likes to use the right-to-left associativity of the ternary operator '? :' to chain conditions (and save lines of code) like this:

Code: Select all

a = b ? c : d ? e : f;

which is equivalent to

Code: Select all

a = b ? c : (d ? e : f);

I learnt this 'trick' reading stockfish, but I prefer not writing code like that, as it takes too much brain power to read.

The rules of C are the way they are for a reason. Well, sometimes it's a bad reason. But in the case of the ternary operator, you can read concatenated ternary operators as "if this is true, this value; otherwise if this other thing is true, this other value, etc.". It's as easy to read as an if-else if-...-else block.

[lucasart]

For example, I've noticed that Marco likes to use the right-to-left associativity of the ternary operator '? :' to chain conditions (and save lines of code) like this:

Code: Select all

a = b ? c : d ? e : f;

which is equivalent to

Code: Select all

a = b ? c : (d ? e : f);

I learnt this 'trick' reading stockfish, but I prefer not writing code like that, as it takes too much brain power to read.

The rules of C are the way they are for a reason. Well, sometimes it's a bad reason. But in the case of the ternary operator, you can read concatenated ternary operators as "if this is true, this value; otherwise if this other thing is true, this other value, etc.". It's as easy to read as an if-else if-...-else block.

I don't advocate not using '?:' or arbitrarly limiting ourselves to not chain the ternary operator. All I'm saying is that chaining '?:' without () is a bit obscure (in reality a,b,c,d,e,f are more complex expressions...). So I simply prefer

Code: Select all

a = b ? c : (d ? e : f);

to

Code: Select all

a = b ? c : d ? e : f;

I would never change my chained '?:' for ugly spaghetti if/else blocks. Heaven forbid! Imagine writing the abode one-liner in Pascal with all the begin/end cruft (just the thought gives me nausea already).

Some people think that () should be put everywhere to avoid mistakes.

Code: Select all

a = ((b) ? (c) : ((d) ? (e) : (f)));

Clearly these people are stupid, but they exist...

[AlvaroBegue]

Some people think that () should be put everywhere to avoid mistakes.

Code: Select all

a = ((b) ? (c) : ((d) ? (e) : (f)));

Yeah, those people write in LISP.

I think chaining ternary operators without parentheses is actually preferable. It allows you to do things like this:

Code: Select all

bool operator<&#40;SomeStruct a, SomeStruct b&#41; &#123;
  return a.first != b.first ? a.first < b.first
       &#58; a.second != b.second ? a.second < b.second
       &#58; a.third != b.third ? a.third < b.third
       &#58; a.fourth != b.fourth ? a.fourth < b.fourth
       &#58; a.fifth < b.fifth;
&#125;

If you add parentheses to that you'll just mess things up.