Nitpicking the D grammar

[Jascha Wetzel]

Declaration vs. ExpressionStatement

struct S
{
     void opAdd(S s) {}
     void opMul(S s) {}
}

void main()
{
     S a, b;
     a * b;  // Error: a is used as a type
     a + b;  // compiles fine
}

The specs state that an expression is disallowed as a statement if it 
has no effect. DMD consequently allows expressions like "a + b" if they 
invoke an overloaded operator, except, and this is my point here, if the 
expression can be parsed as a declaration. In that case DMD prefers the 
declaration.

Disallowing expressions without an effect is nice, but wouldn't a 
warning suffice? After all the compiler can't find all expressions that 
have no effect. Besides, adding for example two integers and not saving 
the result (which is classified as a no-effect-expression) still has the 
effect of changing the eflags register, which may be read in an asm 
block. So it's questionable what "no effect" actually means.

Wouldn't it be more appropriate here to change the specs to
"Expressions that can be interpreted as a declaration, like (a*b), are 
illegal in expression statements. If such an expression is needed, 
casting it to void will make it legal."
(http://www.digitalmars.com/d/statement.html#ExpressionStatement)

and change the no-effect-error into a warning?