DEFINE_BLOCK_TYPE() defines a new block type.
CALL_BLOCK() calls a block.
These use the compiler's native support for blocks if it exists, but otherwise implement the lower-level version. Note that the structure defined by the fall-back versions is NOT a complete definition of the block layout, and copies of this structure should never be instantiated.
This does not allow non-blocks-aware compiles (like GCC) to create blocks, but it does allow them to use blocks. This means that we can implement things like NSArray's -enumerateObjectsUsingBlock: without breaking GCC compatibility. To do so, you'd first need to declare a block type in the header, like this:
DEFINE_BLOCK_TYPE(GSEnumeratorBlock, void, id, NSUInteger, BOOL*);
Then declare the method like this:
- (void)enumerateObjectsUsingBlock: (GSEnumeratorBlock)aBlock;
Finally, implement it like this:
- (void)enumerateObjectsUsingBlock: (GSEnumeratorBlock)aBlock
{
NSUInteger count = 0;
BOOL shouldStop = NO;
for (obj in self)
{
CALL_BLOCK(aBlock, obj, count++, &shouldStop);
if (shouldStop)
{
return;
}
}
}
If you compile this with clang -fblocks then it will work using Clang's native support for blocks. If you compile it with GCC or clang without -fblocks then it will use the other version. Note that this example uses fast enumeration, so will only compile with clang. A proper GNUstep implementation should have some fall-back code for primitive compilers that don't support this either.
git-svn-id: svn+ssh://svn.gna.org/svn/gnustep/libs/base/trunk@29169 72102866-910b-0410-8b05-ffd578937521
