On 29.09.2017 11:12, Don Clugston wrote:
Guess what this prints
----
import std.stdio;
void main()
{
int i = 0;
switch (i) for (i = 8; i < 10; ++i)
{
case 7:
writeln(i);
return;
default: ;
}
}
----
Why does this even compile? It's because the grammar is:
SwitchStatement:
switch ( Expression ) ScopeStatement
and ScopeStatement allows almost anything.
I think the only sane grammar is
SwitchStatement:
switch ( Expression ) BlockStatement
Initially I thought ScopeStatement was accepted in order to enable
Duff's device, but it isn't necessary for that. It might have originally
accepted ScopeStatement to support
E e; switch( e ) with (E) { .... }
Or it may have just been an accident.
It is very likely that this part of the grammar was deliberately copied
from C. It's also consistent with how all other control flow constructs
are parsed.
But regardless of the original motivation, it allows some truly dreadful
semantics.
I don't see what your proposed grammar change accomplishes:
switch(i){
for(i=8;i<10;++i){
case 7:
writeln(i);
return;
default:{}
}
}
I.e., you seem to have misidentified the culprit. Whether or not to the
curly braces are required by the parser has nothing to do with switch
semantics.
Can we disallow this silliness please?
Maybe this specific case can be disallowed during semantic (but I don't
really see why it helps, it mostly just makes the language definition
more complex).
