[cfe-dev] cppcoreguidelines-pro-type-member-init

[Michael Miller via cfe-dev]

Hi all!

I just finished writing a clang-tidy check to flag uninitialized members
variables. I was thus very happy to see the
cppcoreguidelines-pro-type-member-init check land in clang-tidy mainline
recently! The documentation for this clang-tidy check implies it's
targeting "Type.6: Always initialize a member variable." It seems like some
aspects might be missing, though, and I was wondering if there's anyone
working on adding them or if the plan is to keep the current check as is.

Type.6's enforcement section reads:
• Issue a diagnostic for any constructor of a non-trivially-constructible
type that does not initialize all member variables. To fix: Write a data
member initializer, or mention it in the member initializer list.
• Issue a diagnostic when constructing an object of a trivially
constructible type without () or {} to initialize its members. To fix: Add
() or {}.

Right now, the clang-tidy check only seems to address the first bullet
point yet only partially. It flags member variables that are built-ins or
pointers. Based on my reading, it needs to flag any trivially constructible
typed members, not just built-ins and pointers, excepting fully in-class
initialized record types. If the second bullet point were addressed, either
in this check or a separate one, the two together should cover the full
text.

The other thing I wonder about is whether trivially constructible is too
narrow. There are types that are not trivially constructible, at least in
the definition that I know, that still should be flagged:

struct Foo {
  int Bar;
  std::string Baz;
};

Foo is not trivially constructible because Baz has a user defined
constructor, yet a default initialized Foo will leave Bar in an
indeterminate state. Therefore, it seems like we need to initialize any
member that is one of the following:
A. Built-in or pointer type
B. Record type without a user-provided default constructor with at least
one member that needs to be initialized as per these criteria
C. Array of any type matching these criteria*

Is anyone actively working on these aspects of Type.6 or is that something
that I should look into?

* One might prefer arrays to be default initialized for performance reasons
in some cases. Perhaps this should be an option.

Thanks!
Michael Miller
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20160226/a2c694e4/attachment.html>