About BlockDecl

Clang Frontend
1

Hi,

I have two questions about BlockDecl.

1. Is it possible to distinguish the following decls in AST:

^ void (void) { };

^ (void) {};

^{};

2. When is BlockDeclRefExpr used?

Thanks.

2

Hi,

I have two questions about BlockDecl.

1. Is it possible to distinguish the following decls in AST:

^ void (void) { };

^ (void) {};

^{};

Hmm. It doesn't look like BlockDecl currently doesn't store enough source information to distinguish these cases, although I may be wrong.

2. When is BlockDeclRefExpr used?

It's used within a block to refer to a "captured" variable from outside the block. From SemaExpr.cpp:

  // If the identifier reference is inside a block, and it refers to a value
  // that is outside the block, create a BlockDeclRefExpr instead of a
  // DeclRefExpr. This ensures the value is treated as a copy-in snapshot when
  // the block is formed.
  //

For example:

void foo(void) {
  int x = 0;
  ^{ x + 1; }();
}

The 'x' within the block would be BlockDeclRefExpr, as it refers to a "captured" variable outside the block. By default, captured variables are literally copied when the block is created, but if a __block annotation precedes the declaration, the variable is captured by reference. e.g.:

void bar(void) {
  __block int x = 0;
^{ x = x + 1; }();
}

Here 'x' in bar is literally modified by the block.

3

Thanks. That's clear.