WIP: STYLE: Use ImageRegion auto [index, size] = region structured bindings

[N-Dekker]

Replaced initializations of the form:

SizeType size = region.GetSize();
IndexType index = region.GetIndex();

By using structured binding of the form auto [index, size] = region, as was introduced by pull request #4367 commit 72aa9a6 "ENH: ImageRegion support C++17 structured binding"

Did so by Notepad++ Replace in Files, using regular expressions:

Find what: ^([ ]+)const (.*)\w.+[ ]+(\w+) = (.+)\.GetIndex\(\);\r\n\1const \2\w+[ ]+(\w+) = \4\.GetSize\(\);$
Replace with: $1const auto [$3, $5] = $4;

Find what: ^([ ]+)const (.*)\w.+[ ]+(\w+) = (.+)\.GetSize\(\);\r\n\1const \2\w+[ ]+(\w+) = \4\.GetIndex\(\);$
Replace with: $1const auto [$5, $3] = $4;

Find what: ^([ ]+)(.*)\w.+[ ]+(\w+) = (.+)\.GetIndex\(\);\r\n\1\2\w+[ ]+(\w+) = \4\.GetSize\(\);$
Replace with: $1auto [$3, $5] = $4;

Find what: ^([ ]+)(.*)\w.+[ ]+(\w+) = (.+)\.GetSize\(\);\r\n\1\2\w+[ ]+(\w+) = \4\.GetIndex\(\);$
Replace with: $1auto [$5, $3] = $4;

Manually added const whenever the values of the bindings were not modified, excluded ImageIORegion, and removed Index and Size type aliases that are no longer used after this commit.

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When reviewing, it may be helpful to ignore whitespace changes: https://github.com/InsightSoftwareConsortium/ITK/pull/4379/files?w=1

[dzenanz]

Looks good. Remove now unused type definitions to get rid of those warnings for a clean CI.

[N-Dekker]

FYI, I'm considering to postpone this pull request, for the moment. I think it's a nice "proof of principle" on how to use structured bindings with ImageRegion. It looks nice. And it does significantly reduce the amount of boilerplate code. But it appears that the PR will trigger some warnings that I find hard to deal with! Like Microsoft's lnt-accidental-copy, "auto doesn't deduce references. A possibly unintended copy is being made" and Coverity's "AUTO_CAUSES_COPY".

For example, the following line may trigger such a warning (lnt-accidental-copy, AUTO_CAUSES_COPY):

const auto [index, size] = region; // copying

The warning would suggest doing the structured bindings "by reference" instead:

const auto & [index, size] = region; // referencing

But I do not blindly want to follow their suggestion to replace copying with referencing. For a rather small object like ImageRegion, copying is pretty fast already, and it will be even faster when ImageRegion has become trivially copyable (pull request #4344). Whereas referencing potentially makes the code more complicated, as it will potentially introduce more dependencies between variables.

I'm considering a workaround for those warnings, but I'm not sure yet. 🤷

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Update, 3 January, 2024: A workaround against those potential warnings might be coming from the following pull request

• ENH: Add itk::Copy(const T & original), which simply returns a copy #4383

Which would allow: const auto [index, size] = itk::Copy(region) without a warning.

[N-Dekker]

Basically I think this pull request is OK, but if it gets merged, we might still get into a discussion on const auto [index, size] = region (copy) versus const auto & [index, size] = region (reference). I do prefer copying, because an ImageRegion is quite a lightweight object, but my position in favor of copying will be stronger once itk::ImageRegion has become trivially-copyable.

itk::ImageRegion should be trivially-copyable in the future: pull request #4344 commit 1f3bbb6 So maybe we can reconsider using the const auto [index, size] = region syntax in the future! For the time being, I'll just close this pull request.