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Provide a "None" value for convenience when using Optional<T>()

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This implementation of NoneType/None does have some holes but I haven't
found one that doesn't - open to improvement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175696 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Blaikie 2013-02-21 00:27:28 +00:00
parent 06ab2c828a
commit 5c43245bf4
3 changed files with 31 additions and 2 deletions
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27
include/llvm/ADT/None.h Normal file
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@ -0,0 +1,27 @@
//===-- None.h - Simple null value for implicit construction ------*- C++ -*-=//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file provides None, an enumerant for use in implicit constructors
// of various (usually templated) types to make such construction more
// terse.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_NONE_H
#define LLVM_ADT_NONE_H
namespace llvm {
/// \brief A simple null object to allow implicit construction of Optional<T>
/// and similar types without having to spell out the specialization's name.
enum NoneType {
None
};
}
#endif

2
include/llvm/ADT/Optional.h
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@ -16,6 +16,7 @@
#ifndef LLVM_ADT_OPTIONAL_H #ifndef LLVM_ADT_OPTIONAL_H
#define LLVM_ADT_OPTIONAL_H #define LLVM_ADT_OPTIONAL_H
#include "llvm/ADT/None.h"
#include "llvm/Support/Compiler.h" #include "llvm/Support/Compiler.h"
#include "llvm/Support/AlignOf.h" #include "llvm/Support/AlignOf.h"
#include <cassert> #include <cassert>
@ -31,6 +32,7 @@ class Optional {
AlignedCharArrayUnion<T> storage; AlignedCharArrayUnion<T> storage;
bool hasVal; bool hasVal;
public: public:
Optional(NoneType) : hasVal(false) {}
explicit Optional() : hasVal(false) {} explicit Optional() : hasVal(false) {}
Optional(const T &y) : hasVal(true) { Optional(const T &y) : hasVal(true) {
new (storage.buffer) T(y); new (storage.buffer) T(y);

4
lib/Support/LockFileManager.cpp
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@ -31,7 +31,7 @@ LockFileManager::readLockFile(StringRef LockFileName) {
// to read, so we just return. // to read, so we just return.
bool Exists = false; bool Exists = false;
if (sys::fs::exists(LockFileName, Exists) || !Exists) if (sys::fs::exists(LockFileName, Exists) || !Exists)
return Optional<std::pair<std::string, int> >(); return None;
// Read the owning host and PID out of the lock file. If it appears that the // Read the owning host and PID out of the lock file. If it appears that the
// owning process is dead, the lock file is invalid. // owning process is dead, the lock file is invalid.
@ -45,7 +45,7 @@ LockFileManager::readLockFile(StringRef LockFileName) {
// Delete the lock file. It's invalid anyway. // Delete the lock file. It's invalid anyway.
bool Existed; bool Existed;
sys::fs::remove(LockFileName, Existed); sys::fs::remove(LockFileName, Existed);
return Optional<std::pair<std::string, int> >(); return None;
} }
bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) { bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {