Re: "for" statement issue

[Steven Schveighoffer via Digitalmars-d]

On 10/21/16 8:34 AM, Andrei Alexandrescu wrote:
I got a question about what happens with this code:
int j;
for({j=2; int d = 3; } j+d<7; {j++; d++;}) {
}

My first instinct was that that won't compile but it surprisingly does.
And it loops forever.

So the grammar according to
https://dlang.org/spec/grammar.html#ForStatement is:

ForStatement:
    for ( Initialize Testopt ; Incrementopt ) ScopeStatement

Initialize:
    ;
    NoScopeNonEmptyStatement

NoScopeNonEmptyStatement:
    NonEmptyStatement
    BlockStatement

NonEmptyStatement goes over a bunch of odd places such as case statement
and default statement. And then BlockStatement is the matched case:

BlockStatement:
    { }
    { StatementList }

So it seems we have another case in which "{" "}" do not introduce a
scope. Fine. The real problem is with the increment part, which is an
expression. The code { j++; d++; } is... a lambda expression that never
gets used, which completes a very confusing sample.

What would be a good solution to forbid certain constructs in the
increment part of a for statement?

How about in general forbidding lambda statements that aren't called or 
used anywhere?

-Steve