Because I find it really handy to quickly, and visually, check the sanity / logic of something.
In your example, it's really easy to run your eyes down a column and see that one of those values is radically different from the others.
As a trivial example:
int robert_age = 32;
int annalouise_age = 25;
int bob_age = 250;
int dorothy_age = 56;
I find easier to read as:
int robert_age = 32;
int annalouise_age = 25;
int bob_age = 250;
int dorothy_age = 56;
Coding styles are about readability and usability. The columns metaphor works well for some categories of data - that's why spreadsheets are so popular.
This is true if you never change your code. But as soon as I have to add
int rumpelstiltskin_age = 202;
to your code, I already want to throw you out the window for the work I have to do and the diff I have to ruin to keep your "pretty" formatting. Just don't bother.
This ruins the readability and usability of your diffs. Say you need to quickly track down a major bug due to a change in a single constant. With horizontal alignment, the diff might contain any number of changed lines, obscuring the crucial change. There are workarounds that ignore whitespace and word-based diffs, but it's just not worth the trouble IMHO.
The problem I was alluding to occurs when a change causes the amount of alignment spaces to change, which then affects all the lines that have been aligned. Without alignment, the diff would be limited to just the code that was changed.
While I agree diff should be adjusted to accomodate for whitespace diffs more easily by default (it can do that with some options), it's not just a burden on the reviewer. It is also a burden on the programmer.
If you have, say, 50 lines of assignment and you align all the values to the largest one, adding one forces you to update 50 lines. I've been faced with those very situations and that is when I understood how important it is not to align values like that.
I don't why the committer can't leave a message like:
> Formatting change. Use `wdiff` to confirm that changes are just stylistic
The reviewer runs `wdiff` and confirms that the commit is just a formatting change. If the language is not layout-aware, then he will know that none of the changes are "semantic". Now he can look over the changed lines themselves (not necessarily with `diff`; just looking at the changed lines themselves) and see if the change is worth it/in line with the project.
PS: Maybe there should be a "column diff", something that checks that one file uses the same alignment as another file. I'm not able to show it here since HN will truncate spaces between words ( ;) ), but the point is to check if two files uses the same alignment, for example that in
> var v = 12
the next variable declaration, the numbers line up. I don't know if that is worth it, and the check would only be valid for some parts of the files.
Sure the reviewer could run `wdiff`, but it's an extra manual step due to a completely cosmetic and useless formatting style. If you're perusing hundreds of diffs, deciding when to applying whitespace significant vs insignificant diffs is a distraction, and it can't be done automatically.
You can fantasize about better diffs. Why isn't a diff applied directly to the abstract syntax trees of a language, for example? However, I think part of the robustness of version control systems comes from keeping things simple, namely line-based diffs, and with that comes a preference for keeping line-based diffs short.
Indeed, because adjusting version control system to parse ever language under the sun is not a good idea, and that would be required to properly identify strictly formatting-related changes.
The correct term is "horizontal alignment", not "vertical alignment". It's impossible to vertically align code unless you're using a two-dimensional visual programming language.
Terminology Note: Horizontal alignment is the practice of adding a variable number of additional spaces in your code with the goal of making certain tokens appear directly below certain other tokens on previous lines.
This practice is permitted, but is never required by Google Style. It is not even required to maintain horizontal alignment in places where it was already used.
Here is an example without alignment, then using alignment:
private int x; // this is fine
private Color color; // this too
private int x; // permitted, but future edits
private Color color; // may leave it unaligned
Tip: Alignment can aid readability, but it creates problems for future maintenance. Consider a future change that needs to touch just one line. This change may leave the formerly-pleasing formatting mangled, and that is allowed. More often it prompts the coder (perhaps you) to adjust whitespace on nearby lines as well, possibly triggering a cascading series of reformattings. That one-line change now has a "blast radius." This can at worst result in pointless busywork, but at best it still corrupts version history information, slows down reviewers and exacerbates merge conflicts.
The vertical-align CSS property specifies the vertical alignment of an inline or table-cell box.
Values (for inline elements)
Most of the values vertically align the element relative to its parent element:
baseline: Aligns the baseline of the element with the baseline of its parent. The baseline of some replaced elements, like <textarea> is not specified by the HTML specification, meaning that their behavior with this keyword may change from one browser to the other.
sub: Aligns the baseline of the element with the subscript-baseline of its parent.
super: Aligns the baseline of the element with the superscript-baseline of its parent.
text-top: Aligns the top of the element with the top of the parent element's font.
text-bottom: Aligns the bottom of the element with the bottom of the parent element's font.
middle: Aligns the middle of the element with the middle of lowercase letters in the parent.
<length>: Aligns the baseline of the element at the given length above the baseline of its parent.
<percentage>: Like <length> values, with the percentage being a percent of the line-height property. (Negative values are allowed for <length> and <percentage>.)
The following two values vertically align the element relative to the entire line rather than relative to its parent:
top: Align the top of the element and its descendants with the top of the entire line.
bottom: Align the bottom of the element and its descendants with the bottom of the entire line. For elements that do not have a baseline, the bottom margin edge is used instead.
