[llvm-dev] Variable names rule

JD Jones via llvm-dev llvm-dev at lists.llvm.org
Mon Feb 4 09:19:55 PST 2019

I so agree.  I have found scope based coding conventions very useful. My favorite was:

*         Static data member:                       s_<lowerCaseLetterThenCamelCase>

*         Non-static data members:           _<lowerCaseLetterThenCamelCase> (This was allowed by the C++ standard I last read. It’s _<UpperCase> that is reserved)

*         Function argments:                         <lowerCaseLetterThenCamelCase>_

*         Function local variables:                <lowerCaseLetterThenCamelCase>

*         Class/Struct identifiers:                 <UpperCaseLetterThenCamelCase>


Even “smart” IDE’s can become confused – I’ve tried several (all “free”, open source) on the LLVM code base, and they’ve all failed, either finding the wrong thing (that has the same identifier) or not finding the thing (when it most definitely does exist).  If someone knows of a (“free”) IDE that does not get confused by the LLVM code base, please, please advise?


Many thanks!


From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of via llvm-dev
Sent: Monday, February 4, 2019 8:21 AM
To: clattner at nondot.org; Michael.Platings at arm.com
Cc: llvm-dev at lists.llvm.org; nd at arm.com
Subject: Re: [llvm-dev] Variable names rule
Importance: Low


IIRC the last time around there was strong agitation to make function names and variable names look different, which made no sense to me because their contextual syntax makes it blatantly obvious whether a name is a function or a variable. The only possible situation where you could be confused is assigning a function to a function-pointer, which in typical C++ basically you never do that.


I'd much rather have a convention that did not treat all "variables" the same. Instead, distinguish variable names based on scope/lifetime; for example, it's common practice (outside of LLVM) for class data members to have a different/variant convention (trailing underscore, leading "m_") because that data all has a scope/lifetime far beyond the current method.  Local variables and function parameters, by contrast, have comparatively limited scope.  With no immediate visual clue to the difference, I find myself spending a fair amount of time paging around the source and trolling through headers trying to work out which is what.  That is: I find the current convention not very readable.


So, I'm quite happy to have camelCase for variables, but would also like some other distinction within the universe of variable names.


Of course any change to existing conventions would cause some churn and confusion, but we *already* have that, as the current nominal conventions aren't in place in the entire codebase.


Regarding snake_case, LLVM has very limited use of that, and only for things that are (a) substitutes or (b) extensions of STL features.  "iterator_range" for example.  camelCase predominates.




From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Chris Lattner via llvm-dev
Sent: Saturday, February 02, 2019 11:19 PM
To: Michael Platings
Cc: llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> ; nd
Subject: Re: [llvm-dev] Variable names rule




On Feb 2, 2019, at 8:18 PM, Chris Lattner <clattner at nondot.org <mailto:clattner at nondot.org> > wrote:




On Feb 1, 2019, at 6:20 AM, Michael Platings via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org> > wrote:


Hi all,


As application of the naming rules are currently under discussion [1] this seems like a good time to bring this up:


The current variable naming rule [2] states: Variable names should be nouns (as they represent state). The name should be camel case, and start with an upper case letter (e.g. Leader or Boats).

I'm a relatively new arrival to the LLVM codebase and I want to follow the rules wherever I can, but I humbly submit that this rule is suboptimal for readable code.

The rationale given at the time this rule was added was "document the prevailing convention" [3].


I completely agree with you that our variable naming rule is broken.  This discussion has been brought up before (e.g. http://lists.llvm.org/pipermail/llvm-dev/2014-October/077685.html) and hasn’t made any progress - people seem to not be willing to make a change, e.g. saying "the cure is worse than the disease".  I’m personally in favor of Nick’s proposal (linked above) which makes variable names and function names be lower camel case.  


It’s worth noting that at the time, if I recall correctly, I argued against Nick’s proposal.  I’m since come around to see the wisdom of his position and agree that we should have done it.




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