#include <NeverDestroyed.hh>
Public Member Functions | |
template<typename... Args> | |
NeverDestroyed (Args &&... args) | |
Passes the constructor arguments along to T using perfect forwarding. More... | |
NeverDestroyed (const NeverDestroyed &)=delete | |
Deleted copy constructor. More... | |
NeverDestroyed (NeverDestroyed &&)=delete | |
Deleted move constructor. More... | |
~NeverDestroyed ()=default | |
Does nothing. Guaranteed! More... | |
T & | Access () |
Returns the underlying T reference. More... | |
const T & | Access () const |
NeverDestroyed & | operator= (const NeverDestroyed &)=delete |
Deleted copy assignment constructor. More... | |
NeverDestroyed & | operator= (NeverDestroyed &&) noexcept=delete |
Deleted move assignment constructor. More... | |
Detailed Description
template<typename T>
class gz::utils::NeverDestroyed< T >
Originally copied from https://github.com/RobotLocomotion/drake/blob/v0.36.0/common/never_destroyed.h Originally licensed BSD 3-Clause (https://github.com/RobotLocomotion/drake/blob/v0.36.0/LICENSE.TXT) Re-licensed Apache-2.0 with permission from: jwnimmer-tri (https://github.com/gazebosim/gz-utils/pull/31#issuecomment-989173512)
Wraps an underlying type T such that its storage is a direct member field of this object (i.e., without any indirection into the heap), but unlike most member fields T's destructor is never invoked.
This is especially useful for function-local static variables that are not trivially destructable. We shouldn't call their destructor at program exit because of the "indeterminate order of ... destruction" as mentioned in cppguide's Static and Global Variables section, but other solutions to this problem place the objects on the heap through an indirection.
Compared with other approaches, this mechanism more clearly describes the intent to readers, avoids "possible leak" warnings from memory-checking tools, and is probably slightly faster.
Example uses:
The singleton pattern:
A lookup table, created on demand the first time its needed, and then reused thereafter:
In cases where computing the static data is more complicated than an initializer_list, you can use a temporary lambda to populate the value:
Note in particular the ()
after the lambda. That causes it to be invoked.
Constructor & Destructor Documentation
◆ NeverDestroyed() [1/3]
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inlineexplicit |
Passes the constructor arguments along to T using perfect forwarding.
◆ ~NeverDestroyed()
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default |
Does nothing. Guaranteed!
◆ NeverDestroyed() [2/3]
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delete |
Deleted copy constructor.
◆ NeverDestroyed() [3/3]
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delete |
Deleted move constructor.
Member Function Documentation
◆ Access() [1/2]
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inline |
Returns the underlying T reference.
◆ Access() [2/2]
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inline |
◆ operator=() [1/2]
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delete |
Deleted copy assignment constructor.
◆ operator=() [2/2]
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deletenoexcept |
Deleted move assignment constructor.
The documentation for this class was generated from the following file: