A Rust interface for Objective-C blocks.

For more information on the specifics of the block implementation, seeClang's documentation:http://clang.llvm.org/docs/Block-ABI-Apple.html

Invoking blocks

TheBlock struct is used for invoking blocks from Objective-C. For example,consider this Objective-C function:

int32_t sum(int32_t (^block)(int32_t, int32_t)) {    return block(5, 8);}

We could write it in Rust as the following:

unsafefnsum(block:&Block<(i32,i32),i32>)->i32 {block.call((5,8))}

Note the extra parentheses in thecall method, since the arguments must bepassed as a tuple.

Creating blocks

Creating a block to pass to Objective-C can be done with theConcreteBlockstruct. For example, to create a block that adds twoi32s, we could write:

letblock=ConcreteBlock::new(|a:i32,b:i32|a+b);letblock=block.copy();assert!(unsafe {block.call((5,8)) }==13);

It is important to copy your block to the heap (with thecopy method) beforepassing it to Objective-C; this is because ourConcreteBlock is only meantto be copied once, and we can enforce this in Rust, but if Objective-C codewere to copy it twice we could have a double free.