//
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// EXTScope.h
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// extobjc
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//
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// Created by Justin Spahr-Summers on 2011-05-04.
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// Copyright (C) 2012 Justin Spahr-Summers.
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// Released under the MIT license.
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//
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#import "OBSmetamacros.h"
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/**
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*\@onExit defines some code to be executed when the current scope exits. The
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*code must be enclosed in braces and terminated with a semicolon, and will be
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*executed regardless of how the scope is exited, including from exceptions,
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*\c goto, \c return, \c break, and \c continue.
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*
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*Provided code will go into a block to be executed later. Keep this in mind as
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*it pertains to memory management, restrictions on assignment, etc. Because
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*the code is used within a block, \c return is a legal (though perhaps
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*confusing) way to exit the cleanup block early.
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*
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*Multiple \@onExit statements in the same scope are executed in reverse
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*lexical order. This helps when pairing resource acquisition with \@onExit
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*statements, as it guarantees teardown in the opposite order of acquisition.
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*
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*@note This statement cannot be used within scopes defined without braces
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*(like a one line \c if). In practice, this is not an issue, since \@onExit is
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*a useless construct in such a case anyways.
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*/
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#define obs_onExit \
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try {} @finally {} \
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__strong obs_mtl_cleanupBlock_t obs_metamacro_concat(obs_mtl_exitBlock_, __LINE__) __attribute__((cleanup(obs_mtl_executeCleanupBlock), unused)) = ^
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/**
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*Creates \c __weak shadow variables for each of the variables provided as
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*arguments, which can later be made strong again with #strongify.
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*
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*This is typically used to weakly reference variables in a block, but then
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*ensure that the variables stay alive during the actual execution of the block
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*(if they were live upon entry).
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*
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*See #strongify for an example of usage.
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*/
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#define obs_weakify(...) \
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try {} @finally {} \
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obs_metamacro_foreach_cxt(obs_mtl_weakify_,, __weak, __VA_ARGS__)
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/**
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*Like #weakify, but uses \c __unsafe_unretained instead, for targets or
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*classes that do not support weak references.
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*/
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#define obs_unsafeify(...) \
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try {} @finally {} \
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obs_metamacro_foreach_cxt(obs_mtl_weakify_,, __unsafe_unretained, __VA_ARGS__)
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/**
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*Strongly references each of the variables provided as arguments, which must
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*have previously been passed to #weakify.
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*
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*The strong references created will shadow the original variable names, such
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*that the original names can be used without issue (and a significantly
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*reduced risk of retain cycles) in the current scope.
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*
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*@code
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id foo = [[NSObject alloc] init];
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id bar = [[NSObject alloc] init];
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@weakify(foo, bar);
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// this block will not keep 'foo' or 'bar' alive
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BOOL (^matchesFooOrBar)(id) = ^ BOOL (id obj){
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// but now, upon entry, 'foo' and 'bar' will stay alive until the block has
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// finished executing
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@strongify(foo, bar);
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return [foo isEqual:obj] || [bar isEqual:obj];
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};
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*@endcode
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*/
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#define obs_strongify(...) \
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try {} @finally {} \
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_Pragma("clang diagnostic push") \
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_Pragma("clang diagnostic ignored \"-Wshadow\"") \
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obs_metamacro_foreach(obs_mtl_strongify_,, __VA_ARGS__) \
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_Pragma("clang diagnostic pop")
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/** *implementation details follow ***/
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typedef void (^obs_mtl_cleanupBlock_t)();
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void obs_mtl_executeCleanupBlock (__strong obs_mtl_cleanupBlock_t *block);
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#define obs_mtl_weakify_(INDEX, CONTEXT, VAR) \
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CONTEXT __typeof__(VAR) obs_metamacro_concat(VAR, _weak_) = (VAR);
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#define obs_mtl_strongify_(INDEX, VAR) \
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__strong __typeof__(VAR) VAR = obs_metamacro_concat(VAR, _weak_);
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