flexibility of operator spacing / mixing of precedence

[MichaelChirico]

I'm not sure how to capture the issue precisely, but I think the current wording of the style guide around operator spacing can lead to some hard-to-read code:

a_constant + 1 / 12

is IMO pretty hard to read vs

a_constant + 1/12

I think what's going on here is + is lower precedence than /, but they have equal spacing. Removing the spacing around / is a visual cue about operator precedence.

The logic breaks down when we use more complicated expressions with more than two levels of operator precedence:

addend  +  base^exponent / denominator # ??

Perhaps the recommendation in this case could be to use parentheses to limit any sub-expression to at most 2 levels of operator precedence. Maybe overkill.

In any case, I think a simple case where + | - and * | / are mixed could be spelled out pretty easily.

[hadley]

Or if you wanted to make it more specific, it could just be "writing fractions without spaces is also ok".

[hadley]

I'm pretty sure I prefer (a + b) / (c + d) to (a + b)/(c + d), so maybe this only applies to simple fractions?

[luciorq]

a_constant + 1 / 12

is IMO pretty hard to read vs

a_constant + 1/12

I would argue that it is only harder to read for someone already used to writing in that way.

Spaces generally enhance readability.

The specific topic on numeric fractions (1/12 vs. 1 / 12) is just arithmetic thinking bias, treating fractions as a single entity and not an operation.

[MichaelChirico]

I'm pretty sure I prefer (a + b) / (c + d) to (a + b)/(c + d), so maybe this only applies to simple fractions?

I agree with your preference, and it's consistent with my point I think.

There, ( is the high-precedence operator, so the spacing around lower-precedence / is good.

I would argue that it is only harder to read for someone already used to writing in that way.

Spaces generally enhance readability.

The specific topic on numeric fractions (1/12 vs. 1 / 12) is just arithmetic thinking bias, treating fractions as a single entity and not an operation.

I think 1 / 12 is fine by itself, my point in this issue is about mixed precedence.

I think most readers know intuitively that / is higher precedence than +, but the spacing as a nudge is I believe helpful:

x + 1 / 2
# vs
x + 1/2

It's clearer that / operates first. I think it's basically the same as why we allow ^ without spaces:

x + 3 ^ 2
# vs
x + 3^2
## or
x / 3 ^ 2
# vs
x / 3^2

I think the issue is even clearer in expressions with more operators:

a * b + c * d - e * f / g
# vs
a*b + c*d - e*f/g

Since the Google C++ guide was referenced elsewhere, I'll note that's in line with their recommendation:

https://google.github.io/styleguide/cppguide.html#Horizontal_Whitespace

[hadley]

I agree with your preference, and it's consistent with my point I think.
There, ( is the high-precedence operator, so the spacing around lower-precedence / is good.

If I carefully think about it, I can understand your point about high vs low precedence operators, but it's something I'd need to think about every time, so we'd need to figure out a simpler way of framing it in order to include in the style guide.