Introduce mbed::NonCopyable traits

[pan-]

Description

The NonCopyable template class disable auto generation of copy assignment operator and copy constructor for classes inheriting from it.

It avoid the private declaration of the copy assignment operator and copy constructor in favor of an explicit element in the base class list.

It is a good practice to tag non value type as NonCopyable, because it inform of invalid copy operation at compile time.

As an example consider the following code:

class Resource; 

class Foo { 
public:     
    Foo() : _resource(new Resource()) { }
    ~Foo() { delete _resource; } 
private:
    Resource* _resource;
};
 
Foo get_foo();
 
Foo foo = get_foo();

There is a bug in this function, it returns a temporary value which will be
byte copied into foo then destroyed. Unfortunately, internally the Foo class
manage a pointer to a Resource object. This pointer will be released when the
temporary is destroyed and foo will manage a pointer to an already released
Resource.

If the class Foo is marked as NonCopyable then it is not possible to write function with the signature Foo get_foo(); because an error will be generated at compile time.

class Resource; 

class Foo : private mbed::NonCopyable<Foo>{ 
public:     
    Foo() : _resource(new Resource()) { }
    ~Foo() { delete _resource; } 
private:
    Resource* _resource;
};
 

Foo get_foo();
Foo foo = get_foo(); // compile time error 

The extensive documentation as well as the implementation details can be found in the NonCopyable header.

Classes in rtos, platform, event and driver have been either fixed or updated to take advantage of this new traits.

Classes in features have not been touched.

Status

READY

Todos

• Review

[0xc0170]

The jenkins CI fails

Error: TimerEvent.h@31,0: #330-D: “mbed::NonCopyable::NonCopyable(const mbed::NonCopyable &) [with T=mbed::TimerEvent]” (declared at line 157 of “./mbed-os/platform/NonCopyable.h”) is inaccessible

[pan-]

The CI failure is due to a programming error in the ST ble shield library: a Timeout object was incorrectly copied. Detecting this type of programming errors at compile time is the main motivation behind this PR.

I have submitted a fix: ARMmbed/ble-x-nucleo-idb0xa1#27

[pan-]

Since the issue is detected by mbed-os-cliapp, I've also submitted a PR to update the ST BlueNRG library: https://github.com/ARMmbed/mbed-os-cliapp/pull/283

[geky]

This looks great!

Excellent documentation and I find it enjoyable that we already found a bug XD

[pan-]

@0xc0170 the BLUENRG library has been updated in mbed-os cliapp, may you relaunch the tests ?

[0xc0170]

@0xc0170 the BLUENRG library has been updated in mbed-os cliapp, may you relaunch the tests ?

restarted

[bulislaw]

+1

[adbridge]

/morph test

[mbed-bot]

Result: SUCCESS

Your command has finished executing! Here's what you wrote!

/morph test

Output

mbed Build Number: 620

All builds and test passed!