[basic.scope.block] p1 When a component matches multiple items

[xmh0511]

Full name of submitter (unless configured in github; will be published with the issue): Jim X

Each

• selection or iteration statement ([stmt.select], [stmt.iter]),
• substatement of such a statement,
• handler ([except.pre]), or
• compound statement ([stmt.block]) that is not the compound-statement of a handler

introduces a block scope that includes that statement or handler.

[Note 1: A substatement that is also a block has only one scope. — end note]

The note only implies that, when a compound statement is a substatement of a selection or iteration statement, even though it will match the second and the last item, it only be considered as introducing one block scope.

How about a selection or iteration statement A itself is a substatement of another selection or iteration statement? How many block scopes does the statement A introduce? We do not have a note to direct the reading for the case. It is the issue cplusplus/draft#4841

For example, saying

Each

• number that is greater than 5, or
• number that is greater than 10

will give you one score.

If you have a number 20, how many scores will you get? At least, this is ambiguous if we meet the case that matches more than one item.

Moreover, given a more natural example:

There are A, B, and C three students in the classroom, where A's age is 20, B's age is 21, C's age is 19, the teacher wants to do a survey about students' age, the teacher asks each person in the classroom whose age is greater than 10 puts your hands up, then A, B, C all put their hands up. Then, in the second round, the teacher says each person in the classroom whose age is greater than 18 puts her hands up. Only A and B put their hands up. The teacher ask C, what's your age, C says 19, the teacher asks why you didn't put your hands up in the second round??? C says: because I just have put my hands up in the first round. The reason sounds a bit strange.

Back to the issue, the note regarding block itself implies that we could consider a component can introduce more than one block scope if the component matches multiple items.