5.6 Block Statements
1
[A block_statement encloses
a handled_sequence_of_statements optionally
preceded by a declarative_part.]
Syntax
2
block_statement ::=
[
block_statement_identifier:]
[
declare
declarative_part]
begin
handled_sequence_of_statements
end [
block_identifier];
3
If a block_statement
has a block_statement_identifier, then
the identifier shall be repeated after the
end; otherwise, there shall not be an identifier
after the end.
Static Semantics
4
A block_statement that
has no explicit declarative_part has an implicit
empty declarative_part.
4.a
Ramification: Thus, other rules can always
refer to the declarative_part of a block_statement.
Dynamic Semantics
5
{execution (block_statement)
[partial]} The execution of a
block_statement
consists of the elaboration of its
declarative_part
followed by the execution of its
handled_sequence_of_statements.
Examples
6
Example of a block
statement with a local variable:
7
Swap:
declare
Temp : Integer;
begin
Temp := V; V := U; U := Temp;
end Swap;
7.a
Ramification: If task objects are declared
within a
block_statement whose execution is
completed, the
block_statement is not left
until all its dependent tasks are terminated (see
7.6).
This rule applies to completion caused by a transfer of control.
7.b
Within a
block_statement,
the block name can be used in expanded names denoting local entities
such as Swap.Temp in the above example (see
4.1.3).
Wording Changes from Ada 83
7.c
The syntax rule for block_statement
now uses the syntactic category handled_sequence_of_statements.
Sponsored by Ada-Europe