Context sensitivity

[Lutger Blijdestijn]

bearophile wrote:

> I was away.
> 
> This is D code adapted from a blog post about C language:
> http://eli.thegreenplace.net/2011/05/02/the-context-sensitivity-of-
c%E2%80%99s-grammar-revisited/
> 
> 
http://www.reddit.com/r/programming/comments/h23h3/the_context_sensitivity_of_cs_grammar_revisited/
> 
> 
> Three little D2 programs that compile with no errors. Similar code is
> allowed in C too:
> 
> //----------------
> 
> alias int Foo;
> void foo() {
>     Foo bar;
>     float Foo;
> }
> void main() {}
> 
> //----------------
> 
> alias int Foo;
> void foo() {
>     Foo Foo;
>     int bar = Foo + 2;
>     assert (bar == 2);
> }
> void main() {}
> 
> //----------------
> 
> alias char Foo;
> void foo() {
>     int bar = Foo.sizeof, Foo, spam = Foo.sizeof;
>     assert(bar == 1);
>     assert(spam == 4);
> }
> void main() {}
> 
> //----------------
> 
> Note: currently I have put nothing about this in Bugzilla.
> 
> My question is: is it OK to keep allowing such kind of code in D2 too? Or
> is it better to statically forbid it?
> 
> A disadvantage of statically disallowing it is the breakage of some valid
> C code. On the other hand I don't think I want to find code like that in D
> programs.
> 
> Bye,
> bearophile

That's surprising, I didn't know it. I agree it should be statically 
forbidden, which does not violate the principles wrt C compatibility because 
it doesn't silently change semantics. 

Tt also interacts with templates because they can pick up the redefined 
name. Not sure if it's really a problem, it would be interesting to think of 
a situation where this can occur in practice. Maybe with lots of templates, 
ctfe and mixins it can became non-obvious? It sure as hell would be 
confusing to run into such a bug.