Better assert without changing built-in assert

[Andrei Alexandrescu]

On 2/16/11 5:04 AM, Jim wrote:
> Jens Mueller Wrote:
>
>> Hi,
>>
>> I'm trying to improve the assertions. I tried the following
>> auto foo(bool var) {
>> 	return tuple(var, "MyMessage");
>> }
>>
>> void bar(bool var, string text) {
>> }
>>
>> unittest {
>> 	bar(foo(true).expand);
>> 	//assert(foo(true).expand); // won't compile
>> }
>>
>> void main() {}
>>
>> $ dmd -unittest -run file.d
>> Commenting in the assert it fails with
>> "Error: expression
>> tuple(foo(true)._field_field_0,foo(true)._field_field_1) of type (bool,
>> string) does not have a boolean value"
>>
>> assert behaves different when expanding tuples. Any explanations?
>> If one could do the above without writing the expand then it would
>> suggest a nice way of enhancing the build-in assert, I think.
>> If one cannot make it work without the .expand another option may be
>> to overload the built-in assert to handle tuples. This may be related to
>> http://d.puremagic.com/issues/show_bug.cgi?id=5547
>> Then one writes e.g.
>> assert(throws!MyException(expression))
>> or
>> assert(pred!("==")(a, b))
>> What do you think?
>>
>> Jens
>
>
> Or like this:
>
>
> import std.conv;
>
> string cat(T...)(T ts)
> {
> 	string s;
> 	foreach(t; ts)
> 	 s ~= to!string(t) ~ " ";
> 	return s;
> }
>
>
> unittest
> {
> 	...
> 	assert(a==b, cat(a,b));
> }

There's already text in std.conv with the same semantics.

{
    assert(a==b, text(a,b));
}


Andrei