400 lines
12 KiB
Rust
400 lines
12 KiB
Rust
/*!
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A Rust interface for Objective-C blocks.
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For more information on the specifics of the block implementation, see
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Clang's documentation: http://clang.llvm.org/docs/Block-ABI-Apple.html
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# Invoking blocks
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The `Block` struct is used for invoking blocks from Objective-C. For example,
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consider this Objective-C function:
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``` objc
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int32_t sum(int32_t (^block)(int32_t, int32_t)) {
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return block(5, 8);
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}
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```
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We could write it in Rust as the following:
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```
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# use block::Block;
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unsafe fn sum(block: &Block<(i32, i32), i32>) -> i32 {
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block.call((5, 8))
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}
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```
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Note the extra parentheses in the `call` method, since the arguments must be
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passed as a tuple.
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# Creating blocks
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Creating a block to pass to Objective-C can be done with the `ConcreteBlock`
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struct. For example, to create a block that adds two `i32`s, we could write:
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```
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# use block::ConcreteBlock;
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let block = ConcreteBlock::new(|a: i32, b: i32| a + b);
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let block = block.copy();
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assert!(unsafe { block.call((5, 8)) } == 13);
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```
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It is important to copy your block to the heap (with the `copy` method) before
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passing it to Objective-C; this is because our `ConcreteBlock` is only meant
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to be copied once, and we can enforce this in Rust, but if Objective-C code
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were to copy it twice we could have a double free.
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*/
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#[cfg(test)]
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mod test_utils;
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use std::marker::PhantomData;
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use std::mem;
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use std::ops::{Deref, DerefMut};
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use std::os::raw::{c_int, c_ulong, c_void};
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use std::ptr;
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#[repr(C)]
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struct Class {
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_private: [u8; 0],
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}
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#[cfg_attr(any(target_os = "macos", target_os = "ios"),
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link(name = "System", kind = "dylib"))]
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#[cfg_attr(not(any(target_os = "macos", target_os = "ios")),
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link(name = "BlocksRuntime", kind = "dylib"))]
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extern "C" {
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static _NSConcreteStackBlock: Class;
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fn _Block_copy(block: *const c_void) -> *mut c_void;
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fn _Block_release(block: *const c_void);
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}
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/// Types that may be used as the arguments to an Objective-C block.
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pub trait BlockArguments: Sized {
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/// Calls the given `Block` with self as the arguments.
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///
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/// Unsafe because `block` must point to a valid `Block` and this invokes
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/// foreign code whose safety the compiler cannot verify.
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unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R;
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}
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macro_rules! block_args_impl {
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($($a:ident : $t:ident),*) => (
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impl<$($t),*> BlockArguments for ($($t,)*) {
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unsafe fn call_block<R>(self, block: *mut Block<Self, R>) -> R {
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let invoke: unsafe extern "C" fn(*mut Block<Self, R> $(, $t)*) -> R = {
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let base = block as *mut BlockBase<Self, R>;
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mem::transmute((*base).invoke)
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};
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let ($($a,)*) = self;
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invoke(block $(, $a)*)
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}
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}
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);
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}
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block_args_impl!();
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block_args_impl!(a: A);
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block_args_impl!(a: A, b: B);
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block_args_impl!(a: A, b: B, c: C);
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block_args_impl!(a: A, b: B, c: C, d: D);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K);
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block_args_impl!(a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K, l: L);
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#[repr(C)]
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struct BlockBase<A, R> {
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isa: *const Class,
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flags: c_int,
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_reserved: c_int,
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invoke: unsafe extern "C" fn(*mut Block<A, R>, ...) -> R,
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}
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/// An Objective-C block that takes arguments of `A` when called and
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/// returns a value of `R`.
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#[repr(C)]
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pub struct Block<A, R> {
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_base: PhantomData<BlockBase<A, R>>,
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}
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impl<A: BlockArguments, R> Block<A, R> where A: BlockArguments {
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/// Call self with the given arguments.
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///
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/// Unsafe because this invokes foreign code that the caller must verify
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/// doesn't violate any of Rust's safety rules. For example, if this block
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/// is shared with multiple references, the caller must ensure that calling
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/// it will not cause a data race.
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pub unsafe fn call(&self, args: A) -> R {
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args.call_block(self as *const _ as *mut _)
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}
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}
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/// A reference-counted Objective-C block.
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pub struct RcBlock<A, R> {
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ptr: *mut Block<A, R>,
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}
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impl<A, R> RcBlock<A, R> {
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/// Construct an `RcBlock` for the given block without copying it.
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/// The caller must ensure the block has a +1 reference count.
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///
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/// Unsafe because `ptr` must point to a valid `Block` and must have a +1
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/// reference count or it will be overreleased when the `RcBlock` is
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/// dropped.
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pub unsafe fn new(ptr: *mut Block<A, R>) -> Self {
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RcBlock { ptr: ptr }
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}
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/// Constructs an `RcBlock` by copying the given block.
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///
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/// Unsafe because `ptr` must point to a valid `Block`.
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pub unsafe fn copy(ptr: *mut Block<A, R>) -> Self {
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let ptr = _Block_copy(ptr as *const c_void) as *mut Block<A, R>;
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RcBlock { ptr: ptr }
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}
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}
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impl<A, R> Clone for RcBlock<A, R> {
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fn clone(&self) -> RcBlock<A, R> {
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unsafe {
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RcBlock::copy(self.ptr)
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}
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}
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}
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impl<A, R> Deref for RcBlock<A, R> {
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type Target = Block<A, R>;
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fn deref(&self) -> &Block<A, R> {
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unsafe { &*self.ptr }
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}
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}
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impl<A, R> Drop for RcBlock<A, R> {
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fn drop(&mut self) {
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unsafe {
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_Block_release(self.ptr as *const c_void);
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}
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}
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}
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/// Types that may be converted into a `ConcreteBlock`.
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pub trait IntoConcreteBlock<A>: Sized where A: BlockArguments {
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/// The return type of the resulting `ConcreteBlock`.
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type Ret;
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/// Consumes self to create a `ConcreteBlock`.
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fn into_concrete_block(self) -> ConcreteBlock<A, Self::Ret, Self>;
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}
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macro_rules! concrete_block_impl {
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($f:ident) => (
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concrete_block_impl!($f,);
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);
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($f:ident, $($a:ident : $t:ident),*) => (
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impl<$($t,)* R, X> IntoConcreteBlock<($($t,)*)> for X
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where X: Fn($($t,)*) -> R {
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type Ret = R;
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fn into_concrete_block(self) -> ConcreteBlock<($($t,)*), R, X> {
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unsafe extern "C" fn $f<$($t,)* R, X>(
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block_ptr: *mut ConcreteBlock<($($t,)*), R, X>
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$(, $a: $t)*) -> R
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where X: Fn($($t,)*) -> R {
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let block = &*block_ptr;
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(block.closure)($($a),*)
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}
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let f: unsafe extern "C" fn(*mut ConcreteBlock<($($t,)*), R, X> $(, $a: $t)*) -> R = $f;
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unsafe {
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ConcreteBlock::with_invoke(mem::transmute(f), self)
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}
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}
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}
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);
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}
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concrete_block_impl!(concrete_block_invoke_args0);
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concrete_block_impl!(concrete_block_invoke_args1, a: A);
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concrete_block_impl!(concrete_block_invoke_args2, a: A, b: B);
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concrete_block_impl!(concrete_block_invoke_args3, a: A, b: B, c: C);
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concrete_block_impl!(concrete_block_invoke_args4, a: A, b: B, c: C, d: D);
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concrete_block_impl!(concrete_block_invoke_args5, a: A, b: B, c: C, d: D, e: E);
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concrete_block_impl!(concrete_block_invoke_args6, a: A, b: B, c: C, d: D, e: E, f: F);
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concrete_block_impl!(concrete_block_invoke_args7, a: A, b: B, c: C, d: D, e: E, f: F, g: G);
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concrete_block_impl!(concrete_block_invoke_args8, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H);
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concrete_block_impl!(concrete_block_invoke_args9, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I);
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concrete_block_impl!(concrete_block_invoke_args10, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J);
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concrete_block_impl!(concrete_block_invoke_args11, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K);
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concrete_block_impl!(concrete_block_invoke_args12, a: A, b: B, c: C, d: D, e: E, f: F, g: G, h: H, i: I, j: J, k: K, l: L);
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/// An Objective-C block whose size is known at compile time and may be
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/// constructed on the stack.
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#[repr(C)]
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pub struct ConcreteBlock<A, R, F> {
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base: BlockBase<A, R>,
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descriptor: Box<BlockDescriptor<ConcreteBlock<A, R, F>>>,
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closure: F,
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}
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impl<A, R, F> ConcreteBlock<A, R, F>
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where A: BlockArguments, F: IntoConcreteBlock<A, Ret=R> {
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/// Constructs a `ConcreteBlock` with the given closure.
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/// When the block is called, it will return the value that results from
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/// calling the closure.
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pub fn new(closure: F) -> Self {
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closure.into_concrete_block()
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}
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}
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impl<A, R, F> ConcreteBlock<A, R, F> {
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/// Constructs a `ConcreteBlock` with the given invoke function and closure.
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/// Unsafe because the caller must ensure the invoke function takes the
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/// correct arguments.
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unsafe fn with_invoke(invoke: unsafe extern "C" fn(*mut Self, ...) -> R,
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closure: F) -> Self {
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ConcreteBlock {
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base: BlockBase {
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isa: &_NSConcreteStackBlock,
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// 1 << 25 = BLOCK_HAS_COPY_DISPOSE
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flags: 1 << 25,
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_reserved: 0,
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invoke: mem::transmute(invoke),
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},
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descriptor: Box::new(BlockDescriptor::new()),
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closure: closure,
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}
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}
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}
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impl<A, R, F> ConcreteBlock<A, R, F> where F: 'static {
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/// Copy self onto the heap as an `RcBlock`.
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pub fn copy(self) -> RcBlock<A, R> {
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unsafe {
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let mut block = self;
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let copied = RcBlock::copy(&mut *block);
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// At this point, our copy helper has been run so the block will
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// be moved to the heap and we can forget the original block
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// because the heap block will drop in our dispose helper.
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mem::forget(block);
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copied
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}
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}
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}
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impl<A, R, F> Clone for ConcreteBlock<A, R, F> where F: Clone {
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fn clone(&self) -> Self {
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unsafe {
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ConcreteBlock::with_invoke(mem::transmute(self.base.invoke),
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self.closure.clone())
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}
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}
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}
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impl<A, R, F> Deref for ConcreteBlock<A, R, F> {
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type Target = Block<A, R>;
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fn deref(&self) -> &Block<A, R> {
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unsafe { &*(&self.base as *const _ as *const Block<A, R>) }
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}
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}
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impl<A, R, F> DerefMut for ConcreteBlock<A, R, F> {
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fn deref_mut(&mut self) -> &mut Block<A, R> {
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unsafe { &mut *(&mut self.base as *mut _ as *mut Block<A, R>) }
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}
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}
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unsafe extern "C" fn block_context_dispose<B>(block: &mut B) {
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// Read the block onto the stack and let it drop
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ptr::read(block);
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}
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unsafe extern "C" fn block_context_copy<B>(_dst: &mut B, _src: &B) {
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// The runtime memmoves the src block into the dst block, nothing to do
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}
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#[repr(C)]
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struct BlockDescriptor<B> {
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_reserved: c_ulong,
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block_size: c_ulong,
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copy_helper: unsafe extern "C" fn(&mut B, &B),
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dispose_helper: unsafe extern "C" fn(&mut B),
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}
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impl<B> BlockDescriptor<B> {
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fn new() -> BlockDescriptor<B> {
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BlockDescriptor {
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_reserved: 0,
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block_size: mem::size_of::<B>() as c_ulong,
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copy_helper: block_context_copy::<B>,
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dispose_helper: block_context_dispose::<B>,
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use test_utils::*;
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use super::{ConcreteBlock, RcBlock};
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#[test]
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fn test_call_block() {
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let block = get_int_block_with(13);
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unsafe {
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assert!(block.call(()) == 13);
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}
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}
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#[test]
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fn test_call_block_args() {
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let block = get_add_block_with(13);
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unsafe {
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assert!(block.call((2,)) == 15);
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}
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}
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#[test]
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fn test_create_block() {
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let block = ConcreteBlock::new(|| 13);
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let result = invoke_int_block(&block);
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assert!(result == 13);
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}
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#[test]
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fn test_create_block_args() {
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let block = ConcreteBlock::new(|a: i32| a + 5);
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let result = invoke_add_block(&block, 6);
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assert!(result == 11);
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}
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#[test]
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fn test_concrete_block_copy() {
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let s = "Hello!".to_string();
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let expected_len = s.len() as i32;
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let block = ConcreteBlock::new(move || s.len() as i32);
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assert!(invoke_int_block(&block) == expected_len);
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let copied = block.copy();
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assert!(invoke_int_block(&copied) == expected_len);
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}
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#[test]
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fn test_concrete_block_stack_copy() {
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fn make_block() -> RcBlock<(), i32> {
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let x = 7;
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let block = ConcreteBlock::new(move || x);
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block.copy()
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}
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let block = make_block();
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assert!(invoke_int_block(&block) == 7);
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}
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}
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