void main returning int - why compiles?

bearophile bearophileHUGS at lycos.com
Sun Jan 2 04:08:27 PST 2011

Manfred Nowak:

> | Expression is allowed even if the function specifies a void return
> | type. The Expression will be evaluated, but nothing will be returned.
> | If the Expression has no side effects, and the return type is void,
> | then it is illegal.  
>   http://www.digitalmars.com/d/2.0/statement.html (cited 01/01/11)
> _and_ foo() is not marked to have no side effects.

Walter has closer my issue with this comment:
>It is not a dangerous corner case, it is a deliberate design choice. It is meant to facilitate writing generic code so that the same code can be generated for void and non-void return values.<

But I don't understand still, I don't buy Walter's explanation still. I write my comments in D.learn because I don't want to fill Bugzilla with too much discussions.

This compiles:

int bar() { return 0; }
void main() {
    return bar();

While this doesn't, and this semantic difference looks like corner case of the general D rule (the good D rule seems that if it's a void function you can't return a value different from void, and if it's not a void function then you must return a value of the right type):

int bar() { return 0; }
void main() {
    auto temp = bar();
    return temp;

If I want to create a void function foo(), and I want to generate code inside it, can't I just avoid to add a "return" statement in the generated code, instead of adding return and then letting the compiler silently ignore an eventually present return value?


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