lhames added a comment.
I prefer the lambda syntax: Locking with an argument requires you to know the
idiom (which wasn't immediately obvious to me), whereas the lambda enforces it
implicitly.
We could also consider writing an atomic access adapter for this (and other
types). That would be generally useful, but would also require more
consideration (i.e. we shouldn't block this patch on that discussion).
================
Comment at: source/Symbol/ClangExternalASTSourceCommon.cpp:24
+template <typename FnType>
+static decltype(std::declval<FnType>()(std::declval<ASTSourceMap&>()))
+WithExclusiveSourceMap(FnType fn) {
----------------
spyffe wrote:
> lhames wrote:
> > Does std::result_of<FnType>::type work as the return type?
> >
> > http://en.cppreference.com/w/cpp/types/result_of
> No, it doesn't. If I change the declaration to
> ```
> template <typename FnType>
> static typename std::result_of<FnType>::type
> WithExclusiveSourceMap(FnType fn) {
> ```
> then the compiler can no longer resolve calls:
> ```
> …/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp:25:1: Candidate
> template ignored: substitution failure [with FnType = (lambda at
> …/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp:39:7)]: implicit
> instantiation of undefined template 'std::__1::result_of<(lambda at
> …/lldb/source/Symbol/ClangExternalASTSourceCommon.cpp:39:7)>'
> ```
Oh right, result_of only works for function types at the moment.
One minor tidy-up would be to use the 'auto' function declaration syntax so
that you can use the name of the functor in the decltype expression, rather
than having to declval one up. i.e.:
static decltype(std::declval<FnType>()(std::declval<ASTSourceMap&>()))
WithExclusiveSourceMap(FnType fn) {
becomes
static auto WithExclusiveSourceMap(FnType fn) ->
declval(fn(std::declval<ASTSourceMap&>())) {
...
Repository:
rL LLVM
https://reviews.llvm.org/D35083
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