http://llvm.org/bugs/show_bug.cgi?id=20534
Bug ID: 20534
Summary: ObjC++ attempts to copy lambdas, preventing capture of
move-only types
Product: clang
Version: unspecified
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: C++1y
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
ObjC++ supports capturing move-only types as x-values if they are in __block
storage. However, if C++14 lambdas are used, it is not possible to capture
move-only types, even though there would be a strong motivation for such.
I'm not sure about the internals of how the conversion of C++ lambda to ObjC
block is done, but perhaps lambdas can also be treated as x-values as well when
being converted?
GCD Example:
Preferred syntax:
void logMessage(std::unique_ptr<LogData> logData)
{
dispatch_async([logData = logData] {
// process logData
});
}
fails due to attempt to copy lambda (presumably into ObjC block).
Workaround syntax:
void logMessage(std::unique_ptr<LogData> logDataArg)
{
__block auto logData = std::move(logDataArg);
dispatch_async(^{
// process logData
});
}
Of course this has several properties that are not ideal given the desired
syntax:
1: More verbose
2: All argument variables have to be copied into a local __block storage
variable manually (typos are easy).
3: Explicit capture semantics of C++ lambas are unavailable.
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