Why not all statement are expressions ?

[David Piepgrass]

>> I'm usually fairly ambivalent about the idea of statements 
>> being
>> expressions, but I would *love* for switch to be usable as an 
>> expression.
>> For instance, in Haxe, you can do stuff like the following, 
>> which I get a
>> ton of use out of and often wish D had:
>>
>> a = switch(b)
>> {
>>     case 1: "foo";
>>     case 2: "bar";
>>     case 3: "baz";
>>     case 4: "whee";
>>     default: "blork";
>> }
>>
>> The D equivalents aren't terrible, but they aren't nearly as 
>> nice.
>
> This won't work anyway. We are talking about language grammar 
> here. If made expression, statement would be of type void. Just 
> like assert is.

I see what you're saying, but this switch expression should 
really be of type string.

I certainly wish more things were expressions. "a = if (x) y; 
else z;" isn't especially useful since we have "a = x ? y : z", 
but consider instead something that doesn't map so easily to an 
expression:

// very loosely based on some Android code I wrote recently
dpWidth = _lastKnownWidth =
     if (window.isVisible()) {
         auto m = context.getResources().getSystemMetrics();
         // final statement as value of "if" expr
         window.getWidth() / m.pixelDensity();
     } else if (_lastKnownWidth != 0)
         _lastKnownWidth;
     else
         screenInfo().getWidth();

Or how about:

auto area = {
     auto tmp = foo.bar(baz);
     tmp.width * tmp.height;
}

I also wish "void" were a first-class type with sizeof==0 for 
maximum efficiency:

     int[void] intSet = [2:(), 3:(), 4:()]

Ditto for size of empty structs. D code should never need 
abominations like the C++ EBCO.