5.1 Blocks

A block in Haxe starts with an opening curly brace { and ends with a closing curly brace }. A block may contain several expressions, each of which is followed by a semicolon ;. The general syntax is thus:

{
	expr1;
	expr2;
	...
	exprN;
}

The value and by extension the type of a block-expression is equal to the value and the type of the last sub-expression.

Blocks can contain local variables declared by var expression, as well as local functions declared by function expressions. These are available within the block and within sub-blocks, but not outside the block. Also, they are available only after their declaration. The following example uses var, but the same rules apply to function usage:

{
	a; // error, a is not declared yet
	var a = 1; // declare a
	a; // ok, a was declared
	{
		a; // ok, a is available in sub-blocks
	}
  // ok, a is still available after
	// sub-blocks	
	a;
}
a; // error, a is not available outside

At runtime, blocks are evaluated from top to bottom. Control flow (e.g. exceptions or return expressions) may leave a block before all expressions are evaluated.

Variable Shadowing

Haxe allows local variable shadowing within the same block. This means that a var or function can be declared with the same name that was previously available in a block, effectively hiding it from the further code:

{
	var v = 42; // declare v
	$type(v); // Int
	var v = "hi"; // declare a new v
	$type(v); // String, previous declaration is not available
}

It might come as a surprise that this is allowed, but it's useful to avoid pollution of local name space and thus prevent accidental usage of a wrong variable.

Note, that the shadowing strictly follows syntax, so if a variable was captured in a closure before it was shadowed, that closure would still reference the original declaration:

{
	var a = 1;
	function f() {
	    trace(a);
	}
	var a = 2;
	f(); // traces 1
}