Struct block_sys::Block_layout

#[repr(C)]
pub struct Block_layout {
    pub isa: *const Class,
    pub flags: block_flags,
    pub reserved: i32,
    pub invoke: Option<unsafe extern "C" fn()>,
    pub descriptor: *const c_void,
}

Fields

isa: *const Class

Class pointer. Always initialised to &_NSConcreteStackBlock for blocks that are created on the stack or &_NSConcreteGlobalBlock for blocks that are created in global storage.

flags: block_flags

Flags. See the block_flags enumerated type for possible values. Contains ref count in Apple and ObjFW.

reserved: i32

Reserved - always initialised to 0 by the compiler (but this is not said in the specification).

Used for the reference count in GNUStep and WinObjC.

invoke: Option<unsafe extern "C" fn()>

The function that implements the block. The first argument is this structure, the subsequent arguments are the block’s explicit parameters. If the BLOCK_USE_SRET & BLOCK_HAS_SIGNATURE flag is set, there is an additional hidden argument, which is a pointer to the space on the stack allocated to hold the return value.

descriptor: *const c_void

The block’s descriptor. The actual type of this is:

match (BLOCK_HAS_COPY_DISPOSE, BLOCK_HAS_SIGNATURE) {
    (false, false) => Block_descriptor_header,
    (true, false) => Block_descriptor,
    (false, true) => Block_descriptor_basic,
    (true, true) => Block_descriptor_with_signature,
}

But it is safe to access this through just Block_descriptor_header.