#631 Enable and resolve warning "Implicit retain of 'self' within blocks"

[Christa Runge]

Project / Build settings / Basic, near the bottom of the page.
The warnings should be analysed carefully if they can introduce race conditions.

[Christa Runge]

See also svn r3929 and r3930 where more such warnings were intentionally introduced, but then the compiler warning was (temp) deactivated.

[Christa Runge]

https://stackoverflow.com/questions/21577711/block-implicitly-retains-self-explicitly-mention-self-to-indicate-this-is-i

a few suggestions:

• if you are just reading the iVar, you can just create a local variable before the block which contains the iVar value and use it
• You can also move all the block logic inside a method and call it inside the block.
• Silence the warning by not incorrectly referencing self. It can create retain cycles.

https://stackoverflow.com/questions/49582124/block-implicitly-retains-self-but-is-it-intended-behaviour?noredirect=1&lq=1

• It's not that self->score.alpha is better than score.alpha—technically, it's the exact same code—it's that it makes it obvious that the block is implicitly retaining self.
• This warning about implicit references to self is useful because in the absence of that, when glancing at code it isn't always obvious which blocks have the risk of introducing strong reference cycles and which don't.
• if you're looking for Objective-C documentation, see Programming with Objective-C: Working with Blocks: Avoid Strong Reference Cycles when Capturing self.

(https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html#//apple_ref/doc/uid/TP40011210-CH8-SW16)

https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Blocks/Articles/00_Introduction.html#//apple_ref/doc/uid/TP40007502

[Christa Runge]

Apple docu - Working with blocks:
https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html#//apple_ref/doc/uid/TP40011210-CH8-SW16

• Blocks can also take arguments and return values just like methods and functions.
• Blocks Can Capture Values from the Enclosing Scope
• the value is captured when the block is defined.
• Only the value is captured, unless you specify otherwise.
• the block cannot change the value of the original variable, or even the captured value (it’s captured as a const variable).
• If you need to be able to change the value of a captured variable from within a block, you can use the 'block' storage type modifier on the original variable declaration. This means that the variable lives in storage that is shared between the lexical scope of the original variable and any blocks declared within that scope. It also means that the block can modify the original value.
• You Can Pass Blocks as Arguments to Methods or Functions
• Blocks are also used for callbacks, defining the code to be executed when a task completes.
• A Block Should Always Be the Last Argument to a Method (best practice); because it makes the method call easier to read if it uses a literal as argument for the block.
• Avoid Strong Reference Cycles when Capturing self. If you need to capture self in a block, such as when defining a callback block, it’s important to consider the memory management implications.
• Blocks Can Simplify Concurrent Tasks